|"Tanning made using rock alum"
method is very old, but still used to tan furs which need to be smooth and elastic.In the
alum tanning, you use aluminus sulphate and rock alum ( double sulphate of aluminus and
potassium) . As these two compounds produce sulphuric acid they also use sodium chloride
to avoid that the skin should swell.In this way the skins don't swell and absort the
aluminium oxide which tans the skins.
The skins are cleaned and drained and put in cold water : 500% of the cleaned skin;
50 gr/liter of sodium chloride
2gr/ liter hydrochloric acid.
20gr/liter rock alum
20 gr/ liter soluble fat to avoid the skins become stingy during the drying
The skins are staying in this solution for 24/48 hours and they must be mixed sometimes
at the end they will be put to drying on some wires hung to wooden poles.After one mounth
they are ready to be used.