Chalk- This is not only a familiar object from school times, but also a witness to eras that passed millions of years ago.

Most of the chalk composition is formed by calcium deposits of the shells of prehistoric microorganisms and protozoan plants. Chalk deposits, including processed ones, are used today in various fields - from the production of paints and food additives to cosmetics.

How did chalk originate?

Chalk is a natural material and is mined as a mineral. It is basically calcium deposits formed from the remains of ancient earthly organisms.

In the production of chalk and chalk-containing products, already processed chalk is used.

Natural chalk deposits often contain various undesirable impurities - stones, sand and various mineral particles. Therefore, chalk extracted from the deposits is broken and mixed with water in such a way as to obtain a suspension.

In this case, heavy impurities sink to the bottom, and light calcium particles are sent to a special tank, where, after adding a special adhesive, they are dried, turning them into chalk with which you can draw.

Raw chalk from chalk quarries is used for construction purposes to produce lime.

We bring to your attention another article about the origin, its composition and medicinal properties.

What is chalk and what does it consist of?

The composition of chalk includes:

• calcium oxide – from 47 to 55%;
• carbon dioxide - up to 43%;
• silicon dioxide – no more than 6%;
• aluminum oxide – up to 4%;
• magnesium oxide – no more than 2% of the total mass of chalk;
• chalk may also contain iron, however, its concentration usually does not exceed 0.5%.

Chalk accumulations

The accumulation of Cretaceous deposits began in the so-called Cretaceous period, covering a period of 80 million years. About 20% of the Earth's sedimentary rocks include chalk.

Chalk deposits:

• To the largest chalk deposits include the White Cliffs of Dover, the chalk caves in the French city of Champagne and the chalk cliffs of Mons Klint in Denmark.
• On the territory of Ukraine Cretaceous mountain deposits up to 600 meters thick are located south of Kharkov.
• The largest deposits in the Voronezh region– Kopanishchenskoye, Rossoshanskoye and Buturlinskoye. The city of Belgorod supposedly got its name thanks to local chalk deposits.

Chalk formation

The formation and accumulation of limestone deposits took place over eighty million years.

Foraminifera- single-celled organisms whose shells served as the basis for the formation of today's Cretaceous deposits. After these protozoans died, their shells sank to the ocean floor, creating foraminiferal limestones.

These formations, along with the remains of unicellular coccolithophorid plants, form part of today's Cretaceous accumulations. The remains of coccolithophores and shells of ancient mollusks, compressed under water pressure, were supplemented by skeletal remains of fish and animals for millions of years.

Despite the fact that back in 1953 scientists announced the predominant role of plants in the formation of limestone rocks, there is still an opinion among ordinary people about the primacy of foraminifera.

Compound

The composition of chalk deposits includes:

• Skeleton fragments– approximately 10%. These are the remains of not only protozoa, but also large multicellular animals.
• Ancient mollusk shells- 10 %. Among them were animals with limestone shells - foraminifera.
• Particles of limescale algae growth– no more than 40%. Most of the limestone deposits, contrary to popular belief, were formed from the remains of the simplest plants - coccolithophores, and not thanks to the shells of foraminifers. Coccolithophores have not become extinct; they thrive in the vast oceans today, taking part in the exchange of carbon between the ocean and the atmosphere.
• Ground crystalline calcite– no more than 50%. These are natural mineral formations of complex origin.
• Insoluble silicates- until 3%. These are minerals of geological origin - sand, rock fragments carried into chalk deposits by wind and water. Properties of chalk

Humidity has a great influence on the properties of chalk, affecting its strength and ductility. An increase in humidity leads to deformation, while in a dry environment chalk can crumble even from slight pressure.

Rock saturated with moisture sticks to construction tools. That is why construction work using calcium carbonate is carried out in countries with hot and arid climates. An excellent example of an ancient limestone structure is the Egyptian pyramid of Cheops (Khufu).

At sub-zero temperatures, the rock is prone to disintegrating into fragments of several millimeters.

Chalk cost

The price of chalk will depend primarily on its type (processing) and purpose:

• for painting on asphalt will cost no more 200-400 rubles per package.
• White crayons without dyes will cost about 100 rubles .
• Farmer's chalk I buy in large quantities, shipping several tons. The cost of each ton of ground chalk is 3000-5000 rubles.
• Price for food chalk, used in medicine and in food additives (E-170) – from 40 to 300 rubles for 100 grams. The stone was also used in medicine).

Application of chalk

Today, chalk is a fairly widespread material for various areas of production.

So, chalk is used in the following areas:

1. Chalk paints used for interior decoration during construction and repair work.
2. Chalk is included in cement mixtures, providing them with softness and elasticity.
3. Ground natural chalk actively used for glass production.
4. Chalk is included in farm feed and is used to fertilize the soil.
5. Chalk is the basis for cosmetics– lipstick, foundation, powder, etc. It is the chalk in the foundation that absorbs excess oil and protects the skin from shine.
6. Chalk is also used for household purposes. as an absorbent and whitening component.
7. Production of tooth powders and pastes also cannot do without the use of chalk.
8. In the production of paper and cardboard products Fine (crushed) chalk is used as a filler and paper brightener. Chalk treated with stearic acid has hydrophobic properties. It is also used in the paper industry. The chalk content in paper improves print quality and reduces the likelihood of wear and tear on the printing equipment.
9. Not long ago, chalk was used to mark the playing field.. The spray that rose into the air after the ball hit the line was easy to see. Today, titanium dioxide is used instead of chalk.
10. To remove sweat and reducing the risk of slipping, chalk is still used in sports such as weightlifting, gymnastics and rock climbing today.

Is it possible to eat chalk?

A lack of calcium and other beneficial microelements can lead to a desire to eat chalk. During pregnancy and anemia, some people have a strong craving for eating chalk, so the question of the safety of this mineral for the body arises among many.

Of course, one or two small pieces of pure chalk will not cause much harm to the body. However, it must be remembered that chalk without impurities is not available for free sale and it is practically impossible to get it, except perhaps in a pharmacy in the form of calcium gluconate. The most common product, “school chalk,” is produced with glue and various dyes that are toxic to the body.

Consuming chalk in large quantities can cause calcification of blood vessels, the formation of kidney stones and cause problems with the digestive tract.

In addition to the harmful effects of the impurities that make up construction and office chalk, it is characterized by oxidation when interacting with gastric juice, turning it into a harmful chemical reagent.

What to do if you want to eat chalk?

The desire to eat chalk is often a signal of a lack of calcium in the body. The reasons for its deficiency may be a monotonous diet, prolonged stress conditions, weakening of the body after serious illnesses and pregnancy.

Considering that during pregnancy it is calcium that is the basis for the formation of the child’s nervous and skeletal system, the deficiency of this mineral must be replenished. In this case, a varied diet cannot completely solve the problem, so doctors strongly recommend taking special vitamin complexes during pregnancy.

Due to the fact that the neural tube of the fetus is formed in the early stages, in order to minimize the risks of abnormal development, it is necessary to start taking vitamins while planning pregnancy. Anemia and calcium deficiency in the body often appear with heavy and long periods.

For symptoms of severe calcium deficiency (convulsions, noticeable deterioration and pallor of the skin and hair) You can take calcium gluconate tablets. Unlike stationery and other types of industrial chalk, they are safe, however, with prolonged use they can lead to constipation.

As a rule, the craving for eating chalk ends after expanding the diet to include dairy products, chicken eggs and fresh herbs.

In some cases, the desire to eat inedible and inedible substances may be a sign of a mental disorder. The consequences of consuming inedible items are intestinal obstruction and nutritional deficiencies.

Gather everything you need.

Prepare the forms.

Pour the paint into a bowl.

Add plaster.

Pour the chalk into the molds.

Let the chalk dry.

Gather all the ingredients.

• Duct tape.

Prepare the forms.

Crush the egg shells.

Mix the base.

Add food coloring.

Fill out the forms.

Let the chalk dry.

Prepare your ingredients.

Prepare the forms.

Mix water and starch.

Add food coloring.

Pour mixtures into molds.

Let the chalk dry.

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Where did chalk come from and can it be eaten?

Chalk- this is not only a familiar object from school times, it is also a witness to eras that passed millions of years ago.

Most of the chalk composition is formed by calcium deposits of the shells of prehistoric microorganisms and protozoan plants. Chalk deposits, including processed ones, are used today in various fields - from the production of paints and food additives to cosmetics.

How did chalk originate?

Chalk is a natural material and is mined as a mineral. It is basically calcium deposits formed from the remains of ancient earthly organisms.

In the production of chalk and chalk-containing products, already processed chalk is used.

Natural chalk deposits often contain various undesirable impurities - stones, sand, and various mineral particles. Therefore, chalk extracted from the deposits is broken and mixed with water in such a way as to obtain a suspension.

In this case, heavy impurities sink to the bottom, and light calcium particles are sent to a special tank, where, after adding a special adhesive, they are dried, turning them into chalk with which you can draw.

Raw chalk from chalk quarries is used for construction purposes to produce lime.

What is chalk and what does it consist of?

However, the actual composition of chalk includes:

• calcium oxide – from 47 to 55%;
• carbon dioxide - up to 43%;
• silicon dioxide – no more than 6%;
• aluminum oxide – up to 4%;
• magnesium oxide - no more than 2% of the total mass of chalk. Chalk may also contain iron, however, its concentration usually does not exceed 0.5%.

Chalk accumulations

The accumulation of Cretaceous deposits began in the so-called Cretaceous period, covering a period of 80 million years. About 20% of the Earth's sedimentary rocks include chalk.

• The largest chalk deposits include the White Cliffs of Dover, chalk caves in the French city of Champagne and the chalk cliffs of Mons Klint in Denmark.
• In Russia, chalk mountain deposits up to 600 meters thick are located south of Kharkov.
• The largest deposits in the Voronezh region are Kopanishchenskoye, Rossoshanskoye and Buturlinskoye. The city of Belgorod supposedly got its name thanks to local chalk deposits.

Chalk formation

For more than eighty million years, the formation and accumulation of limestone deposits took place.

Foraminifera- single-celled organisms whose shells served as the basis for the formation of today's Cretaceous deposits. After these protozoans died, their shells sank to the ocean floor, creating foraminiferal limestones.

These formations, along with the remains of unicellular coccolithophorid plants, form part of today's Cretaceous accumulations. The remains of coccolithophores and shells of ancient mollusks, compressed under water pressure, were supplemented by skeletal remains of fish and animals for millions of years.

Despite the fact that back in 1953 scientists announced the predominant role of plants in the formation of limestone rocks, there is still an opinion among ordinary people about the primacy of foraminifera.

The composition of chalk deposits includes:

• Skeleton fragments– approximately 10%. These are the remains of not only protozoa, but also large multicellular animals.
• Ancient mollusk shells- 10 %. Among them were animals with limestone shells - foraminifera.
• Particles of limescale algae growth– no more than 40%. Most of the limestone deposits, contrary to popular belief, were formed from the remains of the simplest plants - coccolithophores, and not thanks to the shells of foraminifers. Coccolithophores have not become extinct; they thrive in the vast oceans today, taking part in the exchange of carbon between the ocean and the atmosphere.
• Ground crystalline calcite– no more than 50%. These are natural mineral formations of complex origin.
• Insoluble silicates- until 3%. These are minerals of geological origin - sand, rock fragments carried into chalk deposits by wind and water. Properties of chalk

Humidity has a great influence on the properties of chalk, affecting its strength and ductility. An increase in humidity leads to deformation, while in a dry environment chalk can crumble even from slight pressure.

Rock saturated with moisture sticks to construction tools. That is why construction work using calcium carbonate is carried out in countries with hot and arid climates. An excellent example of an ancient limestone structure is the Egyptian pyramid of Cheops (Khufu).

At sub-zero temperatures, the rock is prone to disintegrating into fragments of several millimeters.

Chalk cost

The price of chalk will depend primarily on its type (processing) and purpose:

• Colored crayons for drawing on asphalt will cost no more 200-400 rubles per package.
• White crayons without dyes will cost about 100 rubles .
• I buy farm chalk in large quantities, shipping it in batches of several tons. The cost of each ton of ground chalk is 3000-5000 rubles.
• Price for edible chalk used in medicine and in food additives (E-170) – from 40 to 300 rubles for 100 grams.

Application of chalk

Today, chalk is a fairly widespread material for various areas of production.

So, chalk is used in the following areas:

1. Chalk paints are used for interior decoration during construction and renovation work.
2. Chalk is part of cement mixtures, providing them with softness and elasticity.
3. Ground natural chalk is actively used for glass production.
4. Chalk is part of farm feed and is used to fertilize the soil.
5. Chalk is the basis for cosmetics - lipstick, foundation, powder, etc. It is the chalk in foundation that absorbs excess oil and protects the skin from shine.
6. Chalk is also used for household purposes as an absorbent and bleaching component.
7. The production of tooth powders and pastes is also not complete without the use of chalk.
8. In the production of paper and cardboard products, finely dispersed (crushed) chalk is used as a filler and paper brightener. Chalk treated with stearic acid has hydrophobic properties. It is also used in the paper industry. The chalk content in paper improves print quality and reduces the likelihood of wear and tear on the printing equipment.
9. Not long ago, chalk was used to mark the playing field. The spray that rose into the air after the ball hit the line was easy to see. Today, titanium dioxide is used instead of chalk.
10. To remove sweat and reduce the risk of slipping, chalk is still used in sports such as weightlifting, gymnastics and rock climbing today.

Is it possible to eat chalk?

A lack of calcium and other beneficial microelements can lead to a desire to eat chalk. During pregnancy and anemia, some people have a strong craving for eating chalk, so the question of the safety of this mineral for the body arises among many.

Of course, one or two small pieces of pure chalk will not cause much harm to the body. However, it must be remembered that chalk without impurities is not available for free sale and it is practically impossible to get it, except perhaps in a pharmacy in the form of calcium gluconate. The most common product, “school chalk,” is produced with glue and various dyes that are toxic to the body.

Consuming chalk in large quantities can cause calcification of blood vessels, the formation of kidney stones and cause problems with the digestive tract.

In addition to the harmful effects of the impurities that make up construction and office chalk, it is characterized by oxidation when interacting with gastric juice, turning it into a harmful chemical reagent.

What to do if you want to eat chalk?

The desire to eat chalk is often a signal of a lack of calcium in the body. The reasons for its deficiency may be a monotonous diet, prolonged stress conditions, weakening of the body after serious illnesses and pregnancy.

Considering that during pregnancy it is calcium that is the basis for the formation of the child’s nervous and skeletal system, the deficiency of this mineral must be replenished. In this case, a varied diet cannot completely solve the problem, so doctors strongly recommend taking special vitamin complexes during pregnancy.

Due to the fact that the neural tube of the fetus is formed in the early stages, in order to minimize the risks of abnormal development, it is necessary to start taking vitamins while planning pregnancy. Anemia and calcium deficiency in the body often appear with heavy and long periods.

For symptoms of severe calcium deficiency (convulsions, noticeable deterioration and pallor of the skin and hair) You can take calcium gluconate tablets. Unlike stationery and other types of industrial chalk, they are safe, however, with prolonged use they can lead to constipation.

As a rule, the craving for eating chalk ends after expanding the diet to include dairy products, chicken eggs and fresh herbs.

In some cases, the desire to eat inedible and inedible substances may be a sign of a mental disorder. The consequences of consuming inedible items are intestinal obstruction and nutritional deficiencies.

Gather everything you need. Besides the ingredients to make chalk, you also need to find a mold. Look around the house or head to your local hobby store to collect the following items:

• Gypsum. You can buy a large pack of plaster of Paris at almost any hobby store. You will need 1/2 cup of gypsum per batch of chalk.
• Tempera paint. This type of paint washes off well, making it convenient to use chalk on the sidewalk or blackboard. Take as many flowers as you like.
• Wax paper. You need it to lay out the chalk molds for it. Without paper, the chalk will stick to them.
• Something that you will use as a form. You can use cardboard toilet paper or paper towel tubes, plastic ice cube trays (unless you intend to use them for other purposes), or any tubes or cardboard molds.
• Electrical tape or tape. You will need to close the bottom of the tube that you will use as a mold to hold the mixture inside.

Prepare the forms. Line pans with wax paper, glossy side up. If you are using tubes, tape one edge to keep the chalk mixture inside.

Pour the paint into a bowl. You need 2 tbsp. spoons of paint per batch of chalk. Measure paint into a bowl, one color per bowl. You can mix paints to create new colors; for example, mix red chalk with yellow to make orange, or blue with yellow to make green. Make sure the total amount of paint per bowl is about 2 tbsp. spoons

Add plaster. Sprinkle 1/2 cup plaster of Paris into each bowl. Stir the mixture thoroughly until all ingredients are completely combined and there are no lumps left.

Add a drop of liquid dish soap. This will make the chalk easier to clean. Simply stir 1-2 drops into each bowl of mixture.

Pour the chalk into the molds. Using a spoon, spoon the mixture into individual molds, one color per mold. Fill the molds as much as you like - the chalk mixture will not expand as it dries. Cover the pans with wax paper when finished.

Let the chalk dry. Transfer the chalk to a dry place to allow the moisture to evaporate. The chalk is ready for use after it is completely dry.

Gather all the ingredients. This method of making chalk includes only natural products that you can find in any store if you suddenly don’t have them on hand. Gather the following items in preparation for your chalk making project:

• Egg shells. If you're lucky enough to have a laying hen on hand, you may have a cache of eggshells just waiting for you to use. If not, try to collect as many shells as possible. If you start preparing in advance, you can ask neighbors and friends to leave them for you.
• Flour. It will thicken the mixture and make the chalk fluffier.
• Food coloring. Both liquid dye and gel are suitable.
• Forms. Use toilet paper tubes or ice cube trays, or any other shape you like.
• Wax paper. You will need it to lay out the forms for it.
• Duct tape.

Prepare the forms. Line your chosen pans with wax paper, glossy side up. If you are using cardboard tubes, tape one end closed.

Crush the egg shells. Make sure they are completely dry before doing this. Use a mortar and pestle or a bowl and the back of a spoon to grind the shells into a fine powder. Make sure that there are no large pieces of shell left; the mixture must be absolutely homogeneous.

Mix the base. Mix two parts flour and one part eggshells in a bowl. Add water, a little at a time, until you have a thick paste. Divide the mixture between bowls, depending on how many different colors you want.

Add food coloring. Mix a few drops of food coloring into each bowl.

Fill out the forms. Spoon the mixture into the molds, one color for each. Cover the pans with wax paper.

• To make it more interesting, try filling one half with one color and the other half with another.

Make a marble crayon: Fill a mold with two (or more) colors, push a wooden stick through both layers and make a few turns in a circle to create swirls.

Let the chalk dry. Wait at least 12 hours before removing the chalk from the mold and using it.

Prepare your ingredients. A simple chalk recipe consists of two things: starch and water in equal proportions. Use food coloring to make more than one color. You can use toilet paper or paper towel tubes or other small containers as molds. You can also make one large sheet of chalk and break it into small pieces.

Prepare the forms. Line the pans with wax paper, making sure to turn the glossy side up. If you are using cardboard tubes as molds, seal one end with tape or duct tape to prevent the chalk from escaping.

Mix water and starch. Add equal amounts of starch and water to the bowl in which you will mix the ingredients. Stir until the mixture becomes thick and smooth. Divide mixture between separate bowls; their number depends on how many different colors you want to get.

Add food coloring. Use a few drops of food coloring to color the mixtures in different bowls. Mix the mixture well in each bowl to distribute the coloring evenly.

Pour mixtures into molds. Using a spoon, spoon mixtures into individual pans. Cover the pans with wax paper.

Let the chalk dry. Wait 12 hours before removing chalk from molds. This chalk is completely natural and completely biodegradable.

• Experiment by adding glitter and other small things.
• Make scented chalk by adding a few drops of essential oil to the mixture before pouring it into molds.
• You can replace the plaster and eggshells with another material containing calcium, such as limestone.

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How to make a stencil with your own hands

How to make Orbeez balls

How to organize your summer holidays so you don't get bored

How to make a book cover

How to smooth out crumpled paper

How to make chalk at home

Colored crayons are a favorite pastime for adults and children. You can use them to draw on the asphalt and walls outside (as long as the janitor doesn’t see), and at home on any surface to create your own artistic masterpieces. This is not egg crackle. there are no difficulties here.

Would you like to try making chalk at home? And one that will be quite fun to draw? After all, such colored chalk will be quite impressive in size, but the quality will remain the same. I wouldn’t mind giving this to someone.

Don't worry, making your own chalk is not at all difficult. Not many things will be useful. And the garbage will also go to waste.

Someone will say: why make something yourself if you can buy it in a store? And we will answer that they don’t sell such colored crayons in stores. And besides, there is nothing more interesting than making such interesting crafts with your child.

We will need toilet paper tubes (cardboard rolls). Several of these cylinders are needed. You also need water, disposable tableware and plaster, which is sold in children's art supplies (or any hardware store). Buy dyes there (you can also make them yourself, read about it here).

You also need parchment paper. If we don't have anything, we'll make do with thick polyethylene. From it we cut out rectangles 5-7 cm wider than the height of the toilet paper cylinder. We wind the paper into a tube and insert it into the roll.

Then we cut out the bottom and seal it with tape.

There should be several such blanks, according to the number of dyes.

We stir the plaster very carefully, trying not to inhale it into ourselves - this is harmful to the lungs. The mixture should have the consistency of thick sour cream. We add our colors there.

Never pour any remaining plaster down the drain! Otherwise, you will need to remove the blockage in the pipe later. and this is not easy.

Then carefully fill the prepared molds, tapping periodically to remove all bubbles. Let it dry for about 2-3 days.

Then comes the fun part - unpacking our homemade chalk.

As you can see, the crayons turn out to be impressive in size.

They are very convenient to draw with. Pack it in a beautiful box and you can safely give it to someone for a holiday.

Chalk is produced by molding white elutriated (ground) chalk and pouring binders into it. This is how any chalk is done, no matter whether it is for wood, fabric or paper. Mineral paints make colored crayons, chalk powder is mixed with a certain mineral paint to get the desired color, this whole mass is mixed in an aqueous solution of wood glue, gum arabica or dextrin, so you can get any shade.

Exhausted chalk (melted chalk) is natural chalk prepared in a special way. And natural chalk is a white sedimentary rock, soft and crumbly, insoluble in water, of organic (zoogenic) origin, mined, not produced.

How is salted chalk made?

To prepare extracted chalk, natural chalk is used. It is broken into pieces, sorted, all impurities are discarded and then ground with water on millstones. The resulting mass settles, and heavy impurities (sand, stones) settle to the bottom. The liquid, containing purer material, is passed into the second vat, then into the third, until all foreign impurities settle to the bottom and are removed. Then the mass is allowed to settle in the vat for quite a long time, the water is drained, and the remaining mass is transferred to boxes with perforated walls, covered with linen. Next, the mass is dried on sieves, and if after drying the chalk is very crumbly, then add a little dextrin solution or glue.

Preparation of colored chalk

Any mineral paint can be used; of course, there are some peculiarities that you need to know, but this is for specialists. Gypsum, alabaster, and also lead white are used as fillers for white crayons, but these materials are too expensive.

Chalk by its nature is hard and free-flowing; to make it soft, soap (in the form of soapy water), oil or wax is added. Finished dried crayons are immersed in oil, which improves their color and makes them softer. Brewer's yeast, glue, gum arabic, and oatmeal paste are also used as a binder for colored crayons.

Preparation is carried out as follows.

Carefully mixed chalk, coloring matter and binder are laid out on the table or on boards, which are first covered with 5-6 sheets of used paper (waste paper). Due to the absorption of a significant part of the moisture by the paper, the mass acquires a thick consistency. When the mass becomes thick enough and you can pick it up without fear of sticking, take a piece the size of a nut, roll it into a ball, and then roll it into a cylinder with your palm. After this, the cylinder is rolled using a smooth board so that it gets a flat and smooth surface. The crayons formed in this way are placed on boards, covered with paper and dried in the shade.

Some chalk recipes:

Blue crayons
Paris blue produces dark shades; when finely ground, it is treated with concentrated sulfuric acid, which discolors it. Subsequent washing with water restores its color and is accompanied by the formation of a fine sediment, which is mixed with an equal amount of chalk and kneaded with water with the addition of a small amount of soap and dextrin.

Red crayons
Mix 4 parts of chalk, 1 part of lime marl by weight and stain with a decoction of cochineal with alum. Very beautiful crayons are obtained by mixing 2 parts red ocher, 1 part carmine, mixed with milk, a decoction of oatmeal or a solution of gum arabica. Ordinary crayons are made from red chalk, red bolus, kolkotar, etc.

Yellow crayons
They are obtained from yellow ocher or chrome yellow, which is used in pure form or ground with honey and mixed with a solution of gum arabic or brewer's yeast.

Green crayons
Green crayons are made from mountain greens, mixed with chalk and brewer's yeast, from a mixture of Prussian blue and chrome yellow, or, finally, from cormorant yellow mixed with ultramarine green or Schweyfurt green (poisonous!).

Black crayons
They are made from willow charcoal or lamp black with the addition of a small amount of Paris blue and adhesives.

Cheap crayons

Cheaper crayons can be prepared by stirring a mixture of good quality light clay and chalk in water. In this way, a porridge-like mass is obtained, to which is added ultramarine for blue crayons, ocher for yellow ones, mummy and cinnabar for red ones, etc. The evenly mixed mass is molded into appropriate forms - from wood or metal. The molds are pre-lubricated with some kind of fat. After shaping, the pieces are left to dry slowly in the air or in lightly heated rooms. After drying, they are ready for use.

You can also make crayons by grinding 1 wt. hours of exhausted chalk with 1 wt. hours of burnt gypsum (which has lost the ability to set) and 0.25 wt. including steatite. Mineral paint of any color is added to the mixture in an appropriate amount. The resulting mixture is mixed with a very weak solution of dextrin into a thick porridge, which is placed on straining cloths to allow excess water to drain. The dried mass is cut into prisms of the desired size and left on gypsum plates to dry. From time to time they turn from side to side.

International Festival “Stars of the New Century” - 2013

Natural Sciences (11 to 13 years old)

“Assessing the quality of school chalk”

MAOU Lyceum No. 82, Chelyabinsk

Scientific adviser:

Geography teacher of the highest category.

Introduction 2

I. The history of chalk and its location in nature 3

II. Chemical composition of chalk and its scope 4

III. School chalk production 5

Practical part

IV. Main indicators of chalk quality 6

V. Qualitative analysis of school chalk 7

VI. Making school crayons at home 8

VII. Sociological survey of 5th grade students of MAOU Lyceum No. 82 9

VIII. Conclusions 11

IX. Used literature 12

X. Applications 13

Introduction

For hundreds of years, people have been using chalk for various purposes. At school, from the first to the eleventh grade, we use chalk for writing on blackboards, of course, we see the inscription on the packaging: non-toxic, made from environmentally friendly products, safe, but when using it we encounter small problems. I decided to independently find out the composition of chalk, its scope of application and determine the quality of school chalk.

Relevance: Today, very serious requirements are placed on school chalk, so it is considered an environmentally friendly and safe product. However, during use, school chalk begins to gather dust, dirty hands, and cause an unpleasant sensation on the respiratory system of the student’s body.

Hypothesis: School chalk may have a negative impact on the health of students.

Goal of the work: To determine the composition of school chalk used in Lyceum No. 82 in Chelyabinsk and to find out its specific effects on the student’s body.

Tasks:

· Study the geographical location of chalk in nature and its composition

· Consider the method of producing school chalk

· Examine chalk samples and find out compliance with the main indicators of chalk quality.

· Using a sociological survey, find out whether contact with chalk has a harmful effect on students’ bodies.

Subject of study: school chalk 3 samples.

Object of study: Respondents of the 5th grade of Lyceum No. 82, 32 people.

Research methods:

Theoretical: comparison method, analysis, generalization.

Practical: research and chemical experiments.

Equipment and reagents: samples of school chalk (three types), acetic acid, test tubes, alcohol solution, iodine solution, distilled water, alcohol lamp.

I.The history of chalk and its location in nature

Not everyone knows that in the beginning chalk was a living organism. In the waters of the ocean there are various types of tiny plants and animals. One of them is a single-celled creature called a furaminifera with a shell made of lime. When they die, they sink to the ocean floor. Over time, they form a thick layer of these shells. Of course, this takes millions of years. Gradually this layer cements and turns into soft calcium carbonate, which we call chalk.1

But there is another way of deposition. Like salt and gypsum, which are deposited on the bottom of seas, lakes, lagoons, due to the evaporation of water. From the subject of geography, we know that various changes have taken place on earth. So the seas dried up and retreated, turning into dry land. A striking example of this is the English Channel. The layers of chalk that were on the seabed were raised above the surface of the sea. The loosest areas have been washed away, leaving high chalk cliffs. In various areas of the world, chalk lies far from the sea, where there once was a sea. An example of this is the states of Kansas, Arkansas, and Texas in the USA. But the best chalk comes from England.2

The extraction and processing of chalk does not cause serious environmental disturbances. Chalk reserves are practically unlimited in many European countries, countries of the former CIS and the Russian Federation. The thick Cretaceous belt extends across the entire European continent, including northern France, southern Britain, Poland, passes through Ukraine and moves into Asia-Syria and the Libyan Desert. Chalk reserves are not evenly distributed across territories: about 50% of the reserves of high-quality chalk without harmful impurities, with a high content of limestone and magnesium, are concentrated in the Russian Federation, about 33% in Ukraine and 12% in Belarus.

There are small deposits in Kazakhstan, Lithuania and Georgia. The total balance reserves of chalk in the Russian Federation are estimated at 3300 million tons with unlimited forecast reserves. The Belgorod region has unlimited chalk resources; in total, 29 chalk deposits have been explored with total reserves of 1000 million tons. The largest chalk deposits are Lebedyanskoye, Stoilenskoye and Logovskoye.

The production of high-quality chalk brands is concentrated in Russia, primarily at chalk factories in the Belgorod region, also in the Bryansk region, large deposits: Fokinskoye, with a content of 75% chalk and 25% clay, is considered natural.

Cretaceous steep slopes near the village. Suponeva on the right bank of the river. The gums expose a layer of sandy chalk of Turanian age (Late Cretaceous), which contains a large number of shell remains

1-Arkady Likum. Everything about everything. Volume 1. Popular encyclopedia for children. From Moscow. 19p.

bivalve inotheram molluscs.

The famous hardness-softness gradation of chalk was developed at Algem. Chalk becomes hard from too much gypsum, and soft from prolonged drying or the use of very high temperatures.

Now it is difficult to imagine that previously all chalk produced was the same. For example: hard chalk is used for drawing on any rough surface, and soft or medium-soft chalk is used on boards, fabric or furniture.

During production, chalk powder is thoroughly mixed with gypsum (white chalk), as well as with dyes (colored). The quality of the chalk depends on the quality of the powder; for example, it should not contain solid particles of gypsum or sand, which then scratch the board when writing. The resulting powder is poured into a barrel, where it is manually diluted with water. The mixture is poured into the matrix and remains there for some time, then the water gradually evaporates, and a chemical reaction occurs that binds the molecular structure of chalk and gypsum. Then the matrix is ​​turned over onto a special lattice tray and “removed” from the crayons. After this, the matrices are washed in a special soap solution because raw crayons will be easier to lag behind. The pallet is placed in a drying cabinet, the chalk is kept there for a certain time, then the finished chalks are sent to the packaging workshop. Packaging is done by hand; good manufacturers have a low percentage of defects. Crayons that break when removing the matrix are immediately removed by workers. Over-dried or under-dried crayons are selected by packers, “under-dried” chalk is returned for drying, and over-dried chalk is returned to production waste .6

IV. Main indicators of chalk quality.

The main indicators of chalk quality include:

Obvious

·Crumbles

Gets your hands dirty

· Purity (white)

· Solid inclusions

Non-obvious

· No traces of PVA glue

· Use of purified water

· Quality of dyes

To consider the obvious indicators of chalk quality, let’s take 3 chalk samples:

Sample of 1-chalk from Algem, Moscow (students in my class use this chalk in lessons near the blackboard)

Sample of 2-chalk from Elikont, Belgorod

Sample of 3-chalk from Pegasus, Klin

According to the indicators, of the three samples, samples No. 1 are the highest quality with good color, low flowability, and soilability.

Sample color, medium flowability.

Sample No. 3 - high flowability, high soilability.

Flowability (can be determined on black fabric)
Marking	Small
Presence of solid inclusions
Has a shape	Bar with rounded edges	Square shaped block	Square shaped block

V. Qualitative analysis of school chalk.

The main component of chalk is calcium carbonate (CaCO3). Natural chalk does not contain any other components. When making crayons, binders, such as starch or gypsum, are added to the chalk powder.

To find out what binders were used to make chalk, a qualitative analysis is carried out.

Experiment No. 1. To determine calcium carbonate in chalk (CaCO3).

· Grind a piece of chalk in a mortar to a powder.

· Pour crushed chalk into a test tube with a glass rod.

· Add a few drops of acetic acid to the test tube.

· We observe a reaction (hissing), carbon dioxide is released.

· We bring a burning splinter, the fire goes out, carbon dioxide does not support combustion.

Conclusion:

Calcium carbonate (CaCO3) interacts with acetic acid, carbon dioxide (CO2) is released, all chalk samples contain calcium carbonate (CaCO3), since when acid is added, carbon dioxide (CO2) is actively released.

Experiment No. 2. Determination of gypsum in chalk.

In a test tube with crushed chalk, add warm water, shake vigorously, add a few drops of acetic acid (acid will dissolve calcium carbonate, but gypsum will not)

There is no test tube, the solution is white and there is a small sediment at the bottom

Test tube gray foam does not settle for a long time

Test tube No. 3 - the solution is gray, does not settle

Conclusion:

Samples No. 2 and No. 3 contain a large amount of gypsum, sample e.

Experiment No. 3. Determination of starch content.

We will detect starch using an alcohol solution of iodine. 2-3 drops of iodine solution were applied to the pieces of chalk under study. The color and iodine should change to blue if starch is present in the samples.

Sample No. 1		Conclusion (is there starch or not?)
No blue coloration	No starch
Sample No. 2	There is no blue coloration, but the color is close to purple	There is no starch, but another substance similar to PVA glue is probably added
Sample No. 3	No blue coloration	No starch

I want to find out what is present in sample No. 2, I take PVA glue, add 3 drops of iodine and the resulting color is close to the color in sample No. 2. Perhaps PVA glue was added to the chalk composition of sample No. 2 during production.

VIMaking school crayons at home.

After I got acquainted with the material about making school chalk, I wanted to try making chalk myself. It turns out that this is not a difficult process, the main thing is to be patient and take into account the correct dosage.

I needed:

Chalk powder, gypsum powder (alabaster), starch, mortar and glass spoon, beaker, ice molds, scales with technical weights (from the chemistry room in the school laboratory), rubber gloves.

From the beginning I am trying to make shaped chalk with the addition of gypsum:

1. You need to weigh 12g. Chalk powder and 18g. Gypsum powder

3. Add a little purified water (Lux water) to the mortar and mix quickly to form a mass similar to sour cream, since gypsum can quickly harden.

Now we are trying to make school chalk with the addition of starch.

1. You need to weigh 12g. Chalk powder and 18g. Starch powder.

2. Mix the resulting mixture thoroughly with a glass rod, then rub it so that there are no lumps.

3. Add a little purified water to the mortar and mix quickly to form a mass similar to sour cream.

4. Pour the resulting mass into an ice tray and dry it in a warm place for several days.

It was noticeable that the color of the mass with the addition of starch was different from the color of the mass with the addition of gypsum, and also the mass with the addition of gypsum hardened quickly, and the mass with the addition of starch only on the second day.

Mission accomplished. It turned out to be chalk! Chalk with gypsum is gray in color, very hard, writes well on the board, but not very bright, and does not crumble. (Receive 1 sample)

Chalk with starch, the color is almost white, but there is a grayish tint, soft, crumbles in the hands, very dusty, but on the board it writes brighter than chalk with plaster, but I would not use such chalk in a lesson. (receiving 2 samples)

VII Csociological survey of students of 5G 82 lyceum.

1. Are you satisfied with the chalk you use to write in class?

2. Please note which of the following do you experience after working with chalk?

A) gets his hands dirty

B) causes dry skin

C) scratches the board or writes poorly

D) nothing

3. What sensations do you experience on the respiratory system when working with chalk?

B) cough

B) sore throat

D) I don’t feel anything

I interviewed 32 students in my class and obtained the following results, which I calculated as percentages (tables in the appendix).

Analysis of questionnaires:

Based on a sociological survey, we can say that 22 students are satisfied with the quality of chalk, 10 students are not satisfied with the quality of chalk.

Scratches the board-21%

Gets your hands dirty - 41%

Causes dry skin - 32%

Sore throat-17%

Sneezing-11%

Do not experience anything - 63% and 10%

Conclusion

Based on the conducted research, the following conclusions can be drawn:

· Not all chalk sold in stores is of good quality.

· Chalk is of great practical importance, as it is used in various areas of our lives.

· While examining the crayons, I learned that they consist of calcium carbonate (natural chalk), gypsum and starch, and possibly other adhesives (PVA glue).

· In qualitative analysis
The safest school chalk is sample No. 1 from the Algem company; it meets all GOST standards (this chalk is used in our lyceum).

· Sample No. 2 may have a negative impact on health, since chalk dust can cause allergic reactions, it is an allergen and it can cause an asthma attack.

· Never taste school chalk.

Analyzing student profiles, I came to the conclusion that school chalk, with constant contact, can have negative health effects, so that there are no such effects:

· After working with chalk, wash your hands with softening soap.

· Wipe chalk from the board only with a damp cloth.

· Frequently wash the cloth and wipe the tray attached to the board.

· Use only good quality chalk.

Despite all the consequences of the influence of school chalk on the body, ordinary chalk and a blackboard are currently safer for health than marker boards, which release esters and cause asthma attacks, and interactive whiteboards cause unnecessary strain on the eyes.

I plan to continue my work; at the moment, a questionnaire has been developed for a sociological survey of teachers at Lyceum No. 82 to find out what effect working with chalk has on the health of teachers.

Bibliography

1. Arkady Likum. Everything about everything. Volume 1. Popular encyclopedia for children. From Moscow. 19p.

2. Chalk/Natural History. Encyclopedic dictionary/comp. .-M. Great Russian Encyclopedia. 20s.

Other sources:

kraeved *****/82/100488/index. ht.

ru/publikatsii/marki-mela-i-in.

Application

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Table of chalk brands and their purposes

Designation	Body brand	Areas of use
MK-2 and MK-3	Lumpy	Lime production
MD-1;MD-2;MM-3	Crushed	Glass, ceramics and other industries.
MM-1;MM-2;MM-3		Glass, ceramics and other industries.
	Ground for animal feeding	For feeding animals
	Ground for feed production	Feed production
	Ground purified	Paint and varnish, chemical and other industries
MMS-1;MMS-2	Ground separated	Cable, paint and varnish, rubber, polymer and other industries
	Ground for chemical industry	Chemical industry
MTD-1;MTD-2;MTD-3;MTD-4	Fine	In the absence of grades MMS-1 and MMS-2, fine chalk is used
МХО-1;МХО-2	Ground chemically purified	Perfume, cosmetics, rubber, medical, food and other industries

Everyone has been familiar with white and colored crayons since childhood. The appearance in Russian schools of modern blackboards, on which you can write with special markers and felt-tip pens, has led to a sharp decrease in the production of school chalk. However, crayons manufacturers are trying to find new sales channels.

School chalk comes in two main types: lump and pressed. The natural chalk used to make school chalks is quarried or extracted from rocks. This raw material is absolutely safe, non-toxic and does not contain foreign impurities. The basis of pressed chalk is calcium sulfate, which is obtained from gypsum. Starch and limestone are used to make school chalk into specific shapes. Lump natural chalk consists almost entirely of calcium carbonate. For the production of school chalk, sorted natural chalk is used.

Colored crayons are produced using a similar technology, the only difference being that various dyes are added to the mass during the production process. The production of chalk for drawing and writing on boards and on asphalt includes several main stages: grinding the raw materials, settling heavy impurities, drying on a wire rack, adding an adhesive, and molding.

To make the highest quality crayons, exhausted chalk (or, as it is also called, melted) is used. To prepare elutriated chalk, natural chalk is broken into pieces, sorted, impurities are removed, and then ground with water on millstones. The resulting mass settles, as a result of which heavy impurities (sand, stones) are deposited at the bottom of the container. Then the liquid with purer raw materials is passed into the second and then into the third vat until all foreign impurities are at the bottom of the tank and are removed. The remaining chalk solution is left to settle for several hours, after which the water is drained, and the remaining mass is transferred to boxes with perforated walls, which are covered with cloth. Then the mass is dried on wire racks. If the chalk crumbles when dried, then add a small amount of dextrin solution or glue to it. Recently, so-called non-crumbling, dust-free crayons have become increasingly popular. They are made using special technology using casein. The main difference between these crayons and ordinary ones is that they do not stain your hands and clothes when used.

Colored crayons must also have a certain hardness. However, when dyes are added to the chalk mass after drying, the chalk becomes too crumbly. Therefore, when making colored chalk, chalk powder is mixed with a certain amount of mineral paints to obtain the desired shade and mixed in an aqueous solution of wood glue, gum arabic or dextrin. In principle, you can use any mineral paint, but keep in mind that some colors will be distorted when mixed with chalk (for example, cormorant, Prussian blue and chrome yellow). Colored crayons can be used not only for drawing on asphalt (in this case they must be very hard), but also for writing on a blackboard. To make the crayons more soft, add soap solution, oil or wax. Finished and dried crayons are dipped in oil, which improves their color and makes them more soft. A mixture of chalk, dye and binder is laid out on a flat surface, which is first covered with several sheets of paper. The paper absorbs a large amount of moisture, as a result of which the chalk mass acquires a thick consistency. When the mass becomes thick enough, a piece the size of a nut is taken from it, and then rolled into a cylinder. At the last stage of molding, the cylinder is rolled with a smooth board to give it a smooth surface. The finished crayons are laid out on boards, covered with paper and dried at room temperature.

This technology is considered quite expensive due to the large amount of manual labor. To reduce the cost of production, crayons are made from a mixture of light clay, water and chalk, to which a dye is then added - ultramarine (for blue crayons), mummy and cinnabar (for red ones), ocher (for yellow ones), etc. The whole mass is evenly mixed and transferred to special wooden or metal forms, pre-greased with fat. After molding, the pieces of chalk are removed from the molds and left to dry in the air or in a weakly heated room.

In addition, crayons can be made by grinding exhausted chalk with burnt gypsum (which does not set when wet) and soapstone. Then mineral paint is added to the mixture, and it is mixed with a weak solution of dextrin. The mass is placed on straining cloths to remove excess moisture. The dried mass is cut into prisms of the required size and left on gypsum plates to dry, turning them over to the other side from time to time.

The degree of drying of chalk and its composition determine the hardness of the product. Harder chalk is used for drawing on asphalt, medium-hard chalk is used for writing on blackboards, and soft chalk is used for tailoring work.

To produce white and colored crayons using these methods, complex, expensive equipment is not required. The total cost of purchasing everything necessary for production will be about 50 thousand rubles. In addition, you will need cardboard packaging for packaging ready-made crayons (white crayons are usually packaged in large boxes of 100 pieces, and colored crayons - in small boxes of 6-12 crayons). The total costs of organizing a small chalk production range from 100 thousand rubles (including the purchase of raw materials). Finished products are supplied to stationery stores, children's art supply stores, specialized stores for schools, as well as directly to public educational institutions.

The main component of chalk is calcium carbonate (CaCO3) - a form of limestone. Limestone deposits are formed from coccoliths - shells of tiny flagellated plates created from the decomposed skeletons of plankton. To make pastel crayons, the basis is calcium sulfate (CaSO4), which is extracted from an evaporite mineral that is formed from salts of ocean water.

Chalk and dehydrated gypsum have similar properties. Pastel crayons also contain clay and oils that bind the components and make the color last. Thanks to this composition, the crayons have a velvety structure, glide smoothly over the surface and do not crumble. Although production pays special attention to removing impurities, a certain amount still remains. The main ones are: silicon, aluminum, iron, phosphorus and sulfur. Manganese, copper, titanium, sodium oxide, potassium oxide, fluorine, arsenic and strontium are present in smaller quantities.

Chalk production process

A limestone quarry is being developed to produce chalk; This is usually open source development. The limestone is then crushed and ground together with water in a ball crusher (a rotating steel drum with water sprayed inside). At this stage, foreign impurities are washed out of the limestone, leaving a pure powder.

The extraction of gypsum is exactly the same as that of limestone. The difference is that the gypsum must be dehydrated to produce calcium sulfate. This happens in a special chamber where the gypsum is heated to a temperature of 116-121 degrees Celsius. When boiling, 12 to 15 percent of its mass is evaporated. Next, the plaster is heated to 204 degrees and in this form is taken out of the chamber. Then the mass is placed in a vibrating screen, where large particles are sifted out. The powder is then washed again, dried, bagged and sent to the chalk manufacturer.

At the crayon factory, the chalk or calcium sulfate is ground again. To produce school crayons, water is added to the mass and brought to the consistency of clay. Then the mass is stamped and cut into bars about 60 cm long, which are placed in a special mold, five pieces each. This form is sent to the oven, where the mass is kept for four days at a temperature of 85 degrees Celsius. Then the hardened crayons are cut into bars 80 mm long. To make colored crayons, pigments are mixed with a dry base, and only after that water is added and the production cycle described above begins.