The time it takes for a paint coat to dry, for example when painting a portrait, depends on heat, light, and the type of oil. There are special catalytic components which, when added to the oil, accelerate the drying time. They are called dryers or driers, what is it? So named special substances, which include salts of different metals - cobalt, lead, manganese. Such dryers are widely used in the manufacture of varnishes and paints for faster hardening. The proportions of the substances that need to be added to the paint depend on its type.
A bit of history
What are driers? Dryers are catalysts (soaps of monocarboxylic acids) necessary for the formation of a film of materials. Their use has more than four thousand years. In those days, natural materials based on manganese, lead and iron were used. Later, in the fourteenth century, copper sulfate began to be used, and already in the sixteenth - zinc compounds, in the nineteenth - lead and desiccants became cobalt-based substances. In the twenties of the last century, it was possible to standardize the presence of metals in the dryer and make them convenient to use.
Structure
What is desiccant - an additive that is attached to the composition of the coating to accelerate drying. It acts as a catalyst, accelerating chemical reactions. The composition of the desiccant may include various metals. And if there are two, then the drying process proceeds even faster. It is quite possible to choose any composition of the dryer. For example, if pure oil dries in a hundred and twenty hours, then an introduction to it:
- manganese reduces this process to twelve;
- lead up to twenty six;
- manganese and lead - up to seven;
- if calcium is added to manganese and lead, then time will be reduced to six.
In practice, mixtures of several metals are most often used. They are divided into:
- primary - cobalt, iron, cerium, manganese, vanadium;
- secondary - zirconium, lead, barium, bismuth, strontium, aluminum;
- auxiliary - potassium, zinc, calcium, lithium.
Use in painting
Desiccants for artistic paints, especially oil paints, are considered an important component that accelerates the drying process. Which usually lasts a long period. The use of dryers reduces the initial drying time of oil paint from five to twelve to one to two days. However, their excessive use contributes to premature aging, cracks and bumps appear on the canvas. Most often, painting uses dryers containing:
- heavy metal oxides - zinc, lead, cobalt, manganese;
- metal salts of unsaturated fatty acids;
Lead white, which is a pigment, contains a heavy metal and also has desiccant properties. Masters use various mixtures of metal-based dryers. The meaning of the word “desiccant” means desiccant, that is, it is a substance that accelerates drying, film formation of coatings.
Different types of dryers used in decorative art
For ease of work with varnishes and oil paints, several types of driers have been developed:
- Aerosol - if you need quick drying of the picture, and it was painted without mixing the dryer with paint, then you can use a spray that not only increases the drying speed, but also protects the paint layer from ultraviolet radiation. Thanks to this effect, the optical effect of painting is preserved over a long period. Desiccant in the form of an aerosol can be used at all stages of work, it mixes well with oil paints.
- Liquid - they are used to improve the drying of oil paints. They are added to the paint on the palette. At all stages of the work, they contribute to the speedy drying of the paint layer and enhance the fluidity of the paint.
- Gel-like - do not affect the viscosity of the paint, interfere evenly. With their help, dense work is dried faster.
Application features
What it is? Desiccant or dryers - a substance, the introduction of which allows manufacturers to diversify the recipe and prepare it for different areas of use. It is added to paints and varnishes in order to accelerate the drying process. In practice, it was proved that the decrease in the time required for drying directly depends on the amount of drier added, that is, there is a certain limit beyond which it is not recommended to add a dryer, since the drying process will slow down.
The amount of desiccant to be entered is indicated in the instructions or on the label. Used dryers are conditionally divided into the following groups:
- Easily soluble - they are introduced into the composition when heated to 150 degrees. Among them are salts of tar and fatty acids.
- Hardly soluble - for better dissolution, they require heating to 250 degrees. These include lead acetic acid, lead red lead, pyrolusite, cobalt acetate.
- Liquid - easily soluble in turpentine, oil and other solvents, it is enough 20 degrees.
The most common dryers
What is a desiccant and where to get it? These are metal compounds (catalysts), which, when added to oils, contribute to quick drying. They can be purchased in stores or cooked at home. The most sought after:
- Cobalt - refers to the main and most used, including at room temperature. The disadvantage is poor-quality deep film formation, the formation of irregularities. Therefore, to create a uniform film, it is used in conjunction with other metals, for example, lead, calcium, and magnesium.
- Lead - has a low activity, therefore it is used together with other desiccants - manganese or cobalt. Accelerates the process of film formation across the entire thickness of the coating layer. The disadvantage is high toxicity, poor compatibility with aluminum pigments, and limited solubility.
- Manganese - in comparison with cobalt it is less effective for materials of atmospheric drying. For thermosetting coatings, as well as for film formation at low temperatures, it gives excellent results. At high humidity, irregularities do not form. Of the shortcomings, a saturated shade that changes the color of the coating should be noted.
- Zirconium - it is called a substitute for lead driers. Compared to other additional dryers, it has good durability, low color and yellowing ability.
- Calcium - manifests itself best when interacting with active desiccants, for example, cobalt.
- Zinc - stabilizes other desiccants, increases gloss, color stability, hardness. A large introduction of this dryer into the material is permitted since. It has a low color.
Home production
What is desiccant - auxiliary compounds that accelerate the drying process when introduced into oil paints. It is possible to cook them yourself. For this:
- Take the porcelain (metal) canister.
- Put 50 grams of rosin in it.
- Melt at a temperature of 250 degrees.
- Stir occasionally.
- After complete melting, add quicklime a little.
- Mix.
- Heating is stopped after obtaining a uniform transparent mixture.
Industrial production
There are several ways to make desiccants in industry:
- The method of deposition or wet - allows you to produce precipitated substances of better quality. Thanks to this, they are widely used. Currently, this method is mainly used for the manufacture of dryers. It was created on the exchange reaction, which takes place in an aqueous solution between an alkaline soap and a metal salt; it does not need heating to a high temperature.
- Dry - with its help get melted dryers. Metal oxides are introduced into rosin, oil and various acids. At high temperatures, soaps (metal salts) are formed. Among the disadvantages of this method are noted: the decomposition of organic (base) substances, in the outcome of which color is lost; high risk of fire.
Disadvantages and advantages of catalysts
Compounds of zinc, lead, cobalt, manganese added to oils to accelerate their drying - this is what siccative.
All types of dryers contribute to:
- darkening of colors;
- loss of elasticity of the oil film;
- the rapid aging of painting.
Therefore, they are added only if necessary.
In paints that dry very slowly, the dryer is added to the production and its further use is not required.
Currently, they are increasingly working with ready-made combinations of dryers based on different metals. They have a small amount of solvents and the optimal composition of metals. The effectiveness of such complexes is significantly higher. Of the advantages, it should be noted:
- globality in use;
- compatibility with different solvents;
- admissibility of work in any weather conditions.
Desiccants for making drying oil
Immediately explain that this is the basis of oil paint. Natural drying oil is made on vegetable oils - hemp, linseed, sunflower and others. Some of them dry in the air, while others partially. However, even drying oils are able to react with oxygen and this interaction occurs very slowly. As a result, you have to wait a long time for the paint to dry. To accelerate the process, a catalyst is added to it. Thus, ordinary drying oil is nothing more than a mixture of oil and drier.
Many dryers are salts of organic acids and they can be prepared on their own. In a metal or porcelain bowl, heat fifty grams of rosin. Then, in small parts, stirring constantly, introduce five grams of calcium oxide into the molten liquid. As a result of transformations, calcium resinate is obtained. If you take fifteen grams of lead oxide, previously ground with linseed oil, and add in small batches to the liquid colophon resin, then lead rubber will come out. Using potassium permanganate and sodium sulfite, manganese oxide can be obtained.
Conclusion
Desiccants are substances that accelerate the drying of materials such as enamels, oil paints, varnishes, primers, drying oils. The most effective are dryers based on cobalt salts, due to which the drying of all layers of paint is carried out evenly. They are added to the paint or applied in a thin layer to the wet work. The desiccant burns out the oil base of the paint and accelerates the drying process. The advantage of cobalt dryers is that they do not impair the intensity and richness of the paint, nor do they affect the color pigment.