Mr Rittel and Others please

Submitted by Len Fabich on 11/1/04 at 6:54 PM. ( )

Mr. Rittels and others.
Greetings from Mt. Village Ak.
I thought I would pose this question on the forum where others could benefit as well.
I am currently working on a project with my students here in western Alaska tanning some moose hides into leather.
My students are preparing powerpoint presentation to explain the process step by step.
We would like to have a professional opinion on what the deliming and bate stage (calcium Hydroxide was used to de-hair) is actually doing from a scienctific (chemical) standpoint.
It is my understanding that the ammonium sulfate stops the action of the lime. We do not have litmus paper that ranges above 6 and my ph meter is broken. Near as we can tell the ph of the ammonium is around 6-7. I am at a loss for explaining exactly what is happening during this stage other than lowering the ph of the hide after the hair has been removed. Could you please give an explanation?
Also I understand the bate process (we are using Oropon N) is utilized to replace enzymes that were leached out during the de-hairing process. Could you expand on this as well.
I appreciate your time. We have been using the forums as a resource for our presentation.
Thanks You
Len Fabich
Teacher Mt.Village Schools
Mt. Village Ak.

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I'll try!

This response submitted by Bruce Rittel on 11/2/04 at 12:21 AM. ( )

The Ammonium Suphate kills further action of the Lime by lowering the PH. Since the Lime is used to weaken and pulp the epidermis and in turn, it removes the hair, if allowed to continue - it would also begin to attack and weaken the main collagen structure of the skin. It is effective only in a very high PH range. One way to prevent it from continuing to work is to simply lower the PH (from a 12-14 range to a 2.5-3.0 range) and effectively the Lime stops working.

Bate is also added to the Ammonium Sulphate to activate and eat away undisolavble fats within the skin structure. This produces a much softer leather. These fats are fats that ordinary degreasers will not remove. However, it does not replace enzymes that were leached out - these are new enzymes that were never present. Years ago Tanners actually used large pits filled with Dog Dung and water to produce these enzymes. They stank terribly but the leather was soft - nowadays these same enymzes are produced synthetically and obviously without the stench. Using Dog Dung was also a good reason most Tanneries back then were also located outside of a Town or City. However if the wind was just right it was considered a "very bad day" in town! This was the case in NYC. The Tanneries were on Long Island and even so - the prevailing winds could ruin an otherwise "good day"!

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