All this stink about alum tanning.
Perhaps Bruce Rittel could explain the difference between ammonium alum and alum. sulphate? Seems that when I first got into this taxidermy thing,ammonium alum was the cure-all.
Return to Tanning Category Menu
Both are considered alum, I have used aluminum sulphate for years.
There are actually 3 different Alums.
Aluminum Sulphate - Iron Free (often called common Alum)
Potassium Aluminum Sulphate (commonly called Potash Alum)
Ammonium Aluminum Sulphate (commonly called Ammonia Alum)
The garment industry has always tended to prefer the Ammonia Alum. It has the most shrinkage, but is also the stretchiest too! Sometimes Potash Alum is also used - but very little because of its availability and the fact that it doesnt quite shrink as much as the Ammoinium Alum.
In Custom Taxidermy tanning - the common Alum is preferred. But it is best to use the Iron Free variety. Otherwise you have to deal with impurities that besides being slightly more yellowish in color, can affect your PHs! Using the Iron Free type will give you more consistent results and PH readings. Common Alum also shrinks the tanned skin - but the least of the 3.
All of the Alums are used to pickle at a 2.78-3.0. Then Soda Ash (Sodium Carbonate) is added to raise the PH to a 3.8 PH where some bonding will take place - this is considered the PH for Tawing (or Tanning - whichever you prefer). The skin or cape is usually soaked in this solution for 3-5 days before being removed, oiled and finished.
One of the major advantages of Alum is that it does shrink the skin! This locks in the fur or hair and offers a nice plump skin for easy shaving! It allows the operator on the Shaving machine to shave a very close shave! And since most of the newer tans do not shrink like Alum - some people still prefer to use it.