Casein color
Casein is a paint ( coll. Color ), in which the pigments with casein are bound. The use of casein paint as casein glue-bound paint is a traditional painting technique in the field of art; since the development of acrylic paints it has lost its importance.
The term poster color , similar to Tempo for paper handkerchiefs, has established and spread as a generic name through the PLAKA brand of Pelikan Holding .
Casein paints are used in artistic and decorative areas because they are easy to mix yourself, often also in kindergartens and schools. The paint has excellent color brilliance and opacity, but it is not necessarily waterproof. If used outdoors, ammonium or lime casein paint should be used.
Components of a casein color
Casein is the main component of milk proteins and is obtained through precipitation . Here, as Quark or skim milk are used, with a low fat content should be worth considering and a higher protein content. The milk fat has a negative effect on the binding force . Milk contains around 3.25% protein, of which the decisive casein makes up 80%. In contrast to other proteins, casein is relatively heat-resistant.
The dried casein powder is hardly soluble in water and is pre-swollen for further use in warm water and usually broken down with a mild lye , for example with deer horn salt - this is ammonium carbonate (ammonium casein) , borax ( borax casein) or lime ( calcium hydroxide ) (lime casein) . Stronger alkalis such as soda ( sodium carbonate ), potash ( potassium carbonate ), sodium hydroxide and potassium hydroxide can also be used, but protective clothing should be used when processing. When breaking down the casein, the maximum addition of caustic should not exceed 25%.
Casein is available ready-to-use from specialist retailers , especially from suppliers of natural colors. Casein in powder form should swell for 30 minutes after mixing with water and then stir again before adding any other ingredients.
Pigments added as colorants must be alkali-resistant.
With fillers such as cellulose , methyl cellulose , kaolin (clay, china clay, etc.) , bentonite and rock flour , especially made of marble or chalk , the paint can be thickened to such an extent that it can be processed almost as thick and opaque as conventional emulsion paints .
For better processing, vegetable oils can be added up to a proportion of about 3% by weight (based on the dry components of the paint before the addition of water). Safflower oil, for example, is used to improve adhesion. The alkalis contained in the oil can wholly or partially saponify and affect the smudge resistance of the paint.
Properties of casein color
Casein is a natural, organic binder . Due to its natural origin, it serves as a breeding ground for bacteria and fungi. If borax is used as a disintegrant, it acts as a preservative and the color can be kept for up to 9 months. However, borax reduces the moisture resistance. When using ammonium carbonate , all excess alkaline components evaporate in the course of time in the form of ammonia . However, ammonium casein can only be kept for a few days. The use of slaked lime also offers good protection against fungal and bacterial attack . Pit lime as a digesting agent cross-links the casein better than borax and does not reduce the water resistance. Therefore, lime casein is the method of choice in wall painting . Small additions of vegetable oils such as linseed oil or linseed oil varnish are common in order to improve processing and adapt the properties.
The durability, the pleasant working and the depth of color with the simultaneous slightly matt drying are considered advantages of the casein colors. The choice of pigments plays a crucial role in the manufacturing process. The majority of the pigments are earth or mineral colors . The colors can be mixed with one another so that a color harmony can easily be established. On the one hand - as in oil painting - you can work “wet-on-wet”, but after rapid drying it can also be glazed using the layering technique.
Depending on the digesting agent used, a casein paint can be waterproof and can therefore be used outdoors. Acid-precipitated casein is mostly used for casein color. Lime casein or ammonium casein should be used to achieve water resistance. The waterproof paints are not alkali-resistant.
The cohesiveness of casein glue is extremely high, so special care is required in processing. Wehlte mentions that drying casein breaks off the glaze of porcelain vessels as well as the enamel of iron bowls and pots. Therefore, when applying a covering layer, ensure that there is sufficient filler to prevent flaking . Glazing colors can be worked out very thinly.
Disadvantages of using casein as a binding agent are the short shelf life in concentrated form and at high temperatures as well as the relatively unpredictable consistency. Casein glue can gel randomly so that it is no longer possible to dilute it. The paste can also suddenly liquefy with a paste-like consistency. However, both shelf life and varying thixotropy can be significantly improved by diluting the glue with water and fillers.
Lime casein - production and processing
Low -fat milk and low-fat quark can be added to pure lime paints to increase opacity and prevent chalking .
Lean quark is mixed in a ratio of 5: 1 with solid lime paste to obtain a translucent binding agent for gluing, priming (thinned), glazing (pigmented & thinned) or for painting (pigmented, filled with fillers & thinned). The resulting casein glue can be used immediately and should be diluted immediately to avoid possible early setting (gelatinization). It should be stored in a cool place and, if diluted slightly, it should be used on the same day, otherwise within a few days. If more than 5 parts of quark are used to 1 part of lime slurry, the paint must be applied thinly so as not to flake off due to the resulting internal tension. In addition, abrasion resistance and weather resistance are reduced, i. H. the color can chalk off. Depending on the lime content, however, the paint can be stored for weeks or even months and the behavior of the paint becomes more predictable.
Traditionally, significantly less low-fat curd cheese was used than lime paste in order to take advantage of the opacity and binding power of the cheaply available lime. Lime paints with small amounts of other binders and fillers are more difficult to process. As a rule, they were applied thinly and in several successive layers to a pre-wetted surface.
history
Milk proteins can already be found in cave paintings . The casein technique was used by the Romans , and the binder can also be found in one of the rock-hewn churches in Lalibela . The technique found its heyday in panel painting on wood, as it places fewer demands on the primer than, for example, oil paints and wall painting , where the color effect is only surpassed by the fresco , but can also be applied to old plaster .
literature
- Kurt Wehlte : Materials and Techniques of Painting , Otto Maier Verlag, Ravensburg 1967, ISBN 3-473-48359-1 (formerly: ISBN 3-473-61157-3 )
- Hans-Werner Bastian: Natural colors mixed themselves , Verlag Heinz Heise 1994, ISBN 3-88229-201-6
- Kurt Schönburg: Natural substances in buildings , properties, application ,: Editor: German Institute for Standardization
swell
- ↑ Atelier ARTani / Anita Windhager, casein paint
- ↑ a b c Safflower Oil , Product Information Art. 370, In: Kreidezeit.de, July 31, 2018
- ↑ Information on borax casein in the Kremer Pigments catalog ( Memento of the original from February 22, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , accessed February 2016
- ↑ Wehlte , p. 465
- ^ Kurt Schönburg: Natural substances in buildings. Beuth Verlag, 2010, ISBN 978-3-410-17355-7 , p. 166 ( limited preview in the Google book search).
- ↑ Recipes and information from Kremer Pigments ( Memento of the original from October 22, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , accessed February 2016
- ↑ today in the museum of Addis Ababa . Wehlte , p. 465
