Lime burning

Limestone firing is carried out by different methods and with different fuel (charcoal or wood).
For frescoes, lime must be burned only with wood, because when charcoal is used, limestone partially turns into gypsum.
When exposed to high temperatures, limestone loses water and charcoal, loses its specific gravity and turns into so-called burnt (unquenched) lime.
To burn lime well, a temperature of 1000 ÷ 1100°C must be reached.
Increasing or decreasing the temperature results in underburning or overburning of the lime. Such lime is not suitable for painting purposes:
overburnt lime does not lasso, while underburnt lime lassoes very slowly or partially.
Pure lime, containing only insignificant amounts of impurities, is characterized by a white hue and forms a good lime cake. Such lime is called "fat", in contrast to lime contaminated with 30 ÷ 40% magnesium, which is called "lean".
Only fatty lime, free of impurities, is used for frescoing.
Burnt lime has the ability to bind chemically with water. There is a process of lime quenching with the release of more heat.
The formation of the so-called "lime cake" - Calcium hydroxide Ca(OH)2.
Chemical process:
CALCIUM = CaCO3 - calcium carbonate,
after firing CaO - calcium oxide,
after quenching Ca(OH)2 - calcium hydroxide,
after drying on the wall - CaO3,
after evaporation of water and absorption of CO2 from the air
turns into a solid.
For painting purposes, lime should be burned with wood.