In these pages we are going to describe the manufacturing cycle of the alum, which was a mineral difficult to find and to manufacture.                                                                                                                                                                         



Just to start this is a block of alumina weighing about 10 kilos, you can see some crystal of the mineral. You must use a lot of these blocks to obtain the alum.




In this picture you can see all the most important points of the manufacturing cycle of the alum.

A) It is the furnace where the mineral was baked; it was generally located near the mines; the mineral was put in the furnace and taken below the furnace after the calcinations.

B) After the calcinations the mineral was carried in some tubs where it was watered plentifully; after 40 days you can find a white sticky mixture; this is brought to the boiler for the following step.

F) This is the boiler where the mixture was boiled ;they mixed it continuously usig a pole: They boiled it for 24 hours; then the impurities fell and, turning on the tap located at the bottom of the boiler, the compound went out to the boxes and crystallizze.

G) Wooden boxes where the compound crystallizes; afther 15 days the crystals are ready and the alum is ready to the loader and sent away.





                                                     This is the finished product taken from the boxes





This is a common usage of the alum you can still find : at the supermarket you can find this stick used to astringe the blood; for examplewhen you shave using a razor blade.



You use the alumm is various ways: to tan skin in some medicines to colour cloth. Here is the old method to tan skins using the "rock alum"that is the name of the alum taken from Tolfa mines.






"Tanning made using rock alum"

This 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.