Mineral paints of white color, made on the basis of lead, are named after the mineral included in their composition - lead whitewash. Depending on the country, time and method of manufacture, lead-based paints were called differently: psimition, Dutch, cerussa, silver foam or simply silver, Klagenfurt, Venetian white, pure lead white, etc.
History of occurrence
Lead white was first described in the writings of the Greek writer Dioscorides as far back as the 4th century BC. Even then they knew about the properties of lead and could produce paints from it. A little later, the production technology was whitewashed, or, as they called them, cerussa, already described by such Roman writers as Vitruvius, Pliny and Theophrastus. In the "new" world, white lead appeared for the first time in Holland already in the Middle Ages. Factory production of whitewash very quickly found wide distribution, and their consumption was constantly growing. Despite this, the scientist Bergman only by the end of the XVIII century was able to discover the chemical composition of whitewash.
As for Russia, the history of the use and manufacture of lead whitewash is not so ancient, only a hundred years ago they began to be produced here. Lead-based paint is produced in large quantities in Yaroslavl, which is considered the center for the manufacture of white. Today, there are several factories that produce well-known whitewash brands that 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 use in painting because of the high toxicity of the product. In exceptional cases, lead-based white is allowed for metal surfaces.
If, however, the use of lead white in the work occurs, then strict adherence to the safety rules prescribed in the case of using such drugs is necessary. Due to the harmful effects on the human body, even white lead is prohibited.
Due to its high toxicity, the use of white is regulated at the legislative level. Thus, the laws of 1909 and 1926 affected the sharp decline in the annual production of these paints in France. Twelve paint and varnish factories of this country produced more than 20,000 tons of white per year, but currently the volume does not exceed 1,000 tons. These laws, unfortunately, apply only to France; in other countries, the use of lead white is not limited by law.
Properties of Lead White
They are made in the form of a white heavy powder having a granular structure. When exposed to vapors of acetic acid on lead, lead white is formed. Their color, judging by the name, is white. Due to the nature of the manufacturing process, the finished product contains a small amount of lead sugar. This affects the smell of lead white, they have a slightly sour aroma, and the ratio of the main acetic salt of lead should not exceed 1% of the total amount of impurities.
Mineral paints, which contain white lead, have a high hiding power and short drying time. Up to 10% of the total weight of the paints is their oil absorption. In the open air, whitewash hardens very quickly, and this happens over the entire thickness of the paint layer. It is thanks to this quality that lead white is so demanded in painting in multi-layer technology and in the production of oil primers.
The composition, and therefore the ability to quickly dry, these paints are easily transferred to other materials, as a result of which even slowly drying paints quickly dry out over their entire layer. They have gained special value for undermining, as they are ideally suited for subsequent staining, while they bind well to subsequent layers and do not crack.
Cons of Using 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, all safety rules must be observed so that the powder is not sprayed. Not only cases of severe poisoning are known, but also deaths.
Lead white can change its light. When exposed to hydrogen sulfide, it first begins to turn brown, and then completely turns black. This happens only if in the composition there was an insufficient amount of a binding element in the white. However, this process is reversible. To acquire a painted surface of its original form, it is necessary to treat the paint with hydrogen peroxide, which can convert black sulfur sulfide to white sulfate.
In an alkaline environment, whitewash is very unstable, which is why they are not suitable for alkaline tempera and frescoes.
In painting, such specificity was noticed. Lead white, triturated with linseed oil, has the ability to change light. If the picture is turned away from the window and directed towards the wall, the paint based on lead white turns yellow, but it can return to its original color if it is exposed to direct sunlight for some time.
Variety whitewashed
To date, various types of white are used. Lead, zinc and titanium are the most common.
Lead - the oldest, they are most often used by old artists. Their advantage is that you can apply transparent layers, and the paint dries very quickly. It has a flexible structure and is more resistant. But the main disadvantage is its toxicity.
Titanium white. They are no less popular with artists and their characteristics are similar to lead white. This paint is the whitest in tone, but its minus is that it is absolutely not transparent and completely paints other tones.
These whitewash are very popular among potters. They intervene directly in the clay, and if this is not enough, then they are applied even from above with a thin layer.
Zinc white. They are not as thick as titanium white and therefore they are used for tinting and applying transparent layers. The downside of this paint is only a long drying time.
Dutch way
This is the very first and oldest method of mining white lead. 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 clay pots, while coiling. Pots should be about 1 liter, and not exceed 20 cm in height. 250 ml of vinegar is poured there. Pots are placed in rows in brick chambers and, covered with layers of horse manure, are folded. A layer of horse manure is covered at the bottom, the first layer of pots is installed on it, from above they are covered with lead plates and boards, and the gaps between the pots are also filled with manure. Thus, the pots are installed in layers to the very top.
During manure fermentation, heat is generated that promotes the evaporation of acetic acid. When oxygen is catalyzed from air, acetic-lead salt is formed, which is converted into carbon-lead salt, which is lead white. The process of separating white from lead plates is the most painstaking, most often machines do this. The most commonly used for these purposes is the Horn device.
German way
The difference between the German method and the Dutch only in details. Lead sheets are not placed 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, a Major device is used for this method.
French way
Tenard proposed a French method for the manufacture of lead white. For him, first a solution of acetic-lead salt is made, through which carbon dioxide is then passed. As a result, white is freed, and the average acetic-lead salt remains in solution. This method is continuous, since in the spent solution, litharge dissolves again, forming the basic salt.
English way
This method of extracting white lead is more complicated, and that is why in recent times less and less used. In horizontal drums, a litharge is moistened with a 1% solution of lead sugar. There he rotates with the help of stirrers. It is treated with a stream of carbon dioxide.
For this method, it is extremely important that there is no impurity in the glute, otherwise the whitewash may acquire an undesirable shade.