Lead-white lead, properties, manufacturing, use, harm to health

Mineral paints of white color, made on the basis of lead, are named after the mineral, which is part of their composition, lead white. Depending on the country, time and method of production, lead-based paints were differently called: psimithion, Dutch, cerussa, silvery foam or simply silvery, Klagenfurt, Venetian white, pure white lead, etc.

History of occurrence

The first bleached lead was described in the writings of the Greek writer Dioscorides in the 4th century BC. Even then they knew about the properties of lead and could make paints from it. A little later the manufacturing technology was white, or, as they were called, cerussa, already described by such Roman writers as Vitruvius, Pliny and Theophrastus. In the "new" light white leaden first appeared in Holland already in the Middle Ages. Factory production of whitewash very quickly found wide distribution, and their consumption was constantly growing. Despite this, scientist Bergman only by the end of the 18th century was able to disclose the chemical composition of whitewash.

As for Russia, the history of the use and manufacture of lead whites is not so ancient, only a hundred years ago they began to be produced from us. Paint based on lead in large quantities is produced in Yaroslavl, which is considered to be the center of the manufacture of white. To date, there are several factories engaged in the manufacture of white brands, which are popular all over the world.

Application area

It is forbidden to use white lead as a solvent for other paints. The same applies to their application in painting works because of the high virulence of the product. In exceptional cases, it is allowed to use lead-based white for metal surfaces.

If nevertheless the use of lead white is used in the work, then strict adherence to the safety rules prescribed in the case of using such preparations is necessary. Because of the harmful effect on the human body, even as a component of paints it is forbidden to use lead white.

Because of the high toxicity, the use of whitewash is regulated at the legislative level. Thus, the laws of 1909 and 1926 influenced the sharp decline in the annual production of these paints in France. Twelve paint and lacquer factories in this country produced more than 20,000 tons of white a year, at the present time the volume does not exceed 1,000 tons. These laws, unfortunately, apply only to the territory of France, in other countries the use of lead whites is not limited to the law.

Properties of lead white

They are produced in the form of a white heavy powder having a granular structure. When exposed to vapors, acetic acid vapor forms lead white. Their color, judging by the name, is white. Due to the nature of the production process, a small amount of lead sugar is contained in the finished product. This affects the smell of lead white, they have a slightly sourish flavor, and the ratio of the basic acetic salt of lead should not exceed 1% of the total amount of impurities.

Mineral paints, which contain lead white, have a great covering power and a short drying time. Up to 10% of the total weight of paints is their oil consumption. In the open air, whitewash very quickly solidifies, and this occurs throughout the thickness of the paint layer. It is thanks to this quality that the lead white is so in demand in painting in multi-layer technique and in the production of oil-based primer coatings.

The composition and, consequently, the ability to dry quickly, these paints are easily transferred to other materials, as a result of which even slowly drying paints dries quickly over their entire layer. They are especially valuable for underpainting, since they are ideal for subsequent staining, but they are well bonded to subsequent layers and do not crack.

Cons in the use of lead white

Along with the obvious advantages of using lead white, they have a number of significant disadvantages.

First of all, it is worth noting the high toxicity of the powder. When grinding, you must follow all safety rules, so that the powder is not sprayed. Not only are cases of severe poisoning known, but also lethal outcomes.

Lead white can change its light. When exposed to hydrogen sulfide, it first begins to burn, and then completely dyed black. This happens only if there is not enough of a binder in the white. However, this process is reversible. To purchase a painted surface of the original form, the paint must be treated with hydrogen peroxide, capable of converting black sulfurous lead to white sulphate.

In the alkaline medium, whitewash is highly unstable, which is why they are not suitable for alkaline tempera and frescoes.

In painting, this specificity was noticed. Lead white, rubbed with linseed oil, have the ability to change light. If the painting is turned away from the window and is directed towards the wall, the paint based on lead white turns yellow, but is able to return the original color if some time it receives direct sunlight.

Variety of whitewash

To date, various types of white are used. Lead, zinc and titanium are the most common.

Lead - the oldest, they are often used by old artists. The plus is that you can apply transparent layers, and the paint dries very quickly. It has a flexible structure and is more stable. But the main disadvantage is its toxicity.

Titanium white. They are no less popular among artists and in characteristics similar to lead white. This paint is the most white in tone, but its minus is that it is absolutely not transparent and completely paints other colors.

These whitewash are very popular with pottery masters. They interfere directly in the clay, and if this is not enough, they are applied still on top with a thin layer.

Zinc white. They are not as thick as titanium white and therefore they are used for toning and applying transparent layers. The drawback of this paint remains only a long time of drying.

Dutch way

This is the very first and oldest method of extraction of lead white. For this method, lead plates with a width of 2-3 mm are cut into strips up to 6 cm long and placed in glazed earthenware pots, while folding the spiral. Pots should be about 1 liter, and do not exceed 20 cm in height. 250 ml of vinegar is poured into the same place. Pots are placed in rows in brick chambers and, interspersed with layers of horse manure, add up. At the bottom cover a layer of horse manure, on it the first layer of pots is established, from above they are covered with lead plates and boards, and the intervals between the pots are also filled with manure. In this way, the pots are installed in layers to the very top.

During the fermentation of manure, heat is released, which contributes to the evaporation of acetic acid. When oxygen is catalyzed from the air, an acetic-lead salt is formed, which converts to lead-cored salt, which is lead white. The separation process is white from the lead plates, the most painstaking, most often machines. The most used for these purposes is the Horn device.

The German way

The difference between the German method and the Dutch is only in details. Lead sheets are not mixed in pots, but are hung in brick and wooden chambers. And then the process of exposure to acetic acid and oxygen is identical. Most often for this method use the device Major.

The French way

Tenar proposed a French method of making lead white. For him, first a solution of acetic-lead salt is made, through which carbon dioxide is subsequently passed through. As a result, white is released, and the average acetic-lead salt remains in the solution. This method is continuous, since in the spent solution the glay dissolves again, forming the basic salt.

English way

This method of extracting lead white is more complex, and that is why lately it has been less and less used. In the horizontal drums, glue, moistened with a 1% solution of lead sugar, is placed. There he rotates with the help of agitators. It is treated with a jet of carbon dioxide.

For this method, it is extremely important that there are no impurities in the glaze, otherwise the whitish may acquire an undesirable shade.