Whitewash is a form of paint which is made from a mixture of slaked lime, chalk, water, and an assortment of other ingredients. It has been used for hundreds of years to paint various structures around the world, and it continues to be utilized in some regions. The primary advantage to whitewash is that it is very inexpensive, but it is also impermanent, forcing people to re-treat whitewashed structures on a frequent basis.
You may also hear whitewash referred to as calcimine or calsomine. The slaked lime is made by heating limestone at high temperatures, turning it into calcium oxide, and then adding water to the mixture to make calcium hydroxide. Typically chalk is added as a whitener. The base materials were historically mixed with a wide range of ingredients like milk, ground rice, glue, egg whites, salt, and flour, among others. To use whitewash, people simply painted it onto the surface which needed whitewashing.
As the whitewash is exposed to carbon dioxide in the air, it cures, acquiring a distinctive bright white color. When first applied, whitewash may seem rather thin; patience is recommended, as it will harden up and turn solid as it cures. Depending on what is added to the whitewash, the whitewash may tend to flake or run in the rain; the addition of glue is often recommended for this reason, as it helps the whitewash to stick. Hide glue flakes, available at craft and construction stores, are ideal for this purpose.
A special form of whitewash known as lime wash is made with pure slaked lime and no adulterants. It can acquire an interesting glint due to small calcite crystals which form as the lime wash cures. Lime washing is sometimes also used to finish furniture; it tends to penetrate very well and produce a pleasing patina.
Whitewash is ideal for the interior of dim structures like barns, because it can brighten up the environment and make it easier to see. It is also often used in homes to create a more reflective environment inside, ensuring that homes stay bright, even in the winter months. Fans of Mark Twain may be aware that whitewash is also used on fences, and it has historically been used on walls as well. This material adheres to a wide variety of surfaces, and it is also possible to paint over it, although the painted design will flake off as the whitewash wears away.