Cracking in the paint
Introduction
The term mineral paints describes paints with mineral binders. There are two relevant mineral binders in the field of paints: lime and silicate.
While lime binders carbonate by reacting with carbon dioxide and water (carbonate formation), silicate binders (generally potassium silicate) react with CO2 and form potassium silicate hydrates in contact with the reactive substances.[1].
Since lime paints (except for the fresco technique) are only weather resistant under certain circumstances, their use is basically reduced to the field of monument conservation. When talking about mineral paints today, one usually refers to silicate paints – or Keim paints (after the inventor, Keimfarben). These paints use potassium silicate (in German, also called “liquid glass”) as a binder.
The special composition of silicate paints gives them specific properties. Silicate mineral paints are characterized by being very durable and weather resistant. They can reach a durability of more than one hundred years. An example of this is the town hall painted with mineral paint in the 19th century in the town of Schwyz, Switzerland.
History
Alchemists, in search of the "Philosopher's Stone" (making gold), discovered pearls of crystalline brilliance among the remains of bonfires. Sand mixed with potassium carbonate and heat melts and becomes potassium silicate beads. The first primitive windows, small and round, were made of potassium silicate. The first industrial production of potassium silicate took place in the century by Van Baerle in Gernsheim and by Johann Gottfried Dingler in Augsburg. The first attempts to manufacture paints with potassium silicate were made by Johann Nepomuk von Fuchs. The façade of the Munich art gallery was painted around 1850 by the painters Kaulbach and Schlotthauer. By using pigments not suitable for silicatization (earth pigments), the murals were lost due to the rain.
Silicate mineral paints were patented in 1878 by the craftsman and researcher Adolf Wilhelm Keim) and are manufactured to this day by the successor company Keimfarben in Diedorf near Augsburg.
Also V. van Baerle, once supplier of potassium silicate to A.W. Keim tried to make silicate paints. His experiments lasted for years until he matured, and he too finally obtained good results. The Silinwerk van Baerle company from Gernsheim am Rhein) and the Keimfarben company from Diedorf near Augsburg became renowned manufacturers.[2].