I was going through some tanned skins the other day and there was a fox and a mink that all but fell appart in my hand. It reminded me of the question that I wanted to ask. They where tanned by a big name tannery in California.
What can I do to keep the acid rot from happening?
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Alum will cause dry rot. So will sodium sulfate. So will 'red rot'. So will bleaching agents, even peroxide. So will removal of the calcium ions in too strong a pickle in the absence of alum. All leather dry rots; chrome-tanned leather dry rots the most slowly but even it will succumb.
There is only one way to slow it down: cold furrier storage. Put all your pelts, capes, and coats in to a freezer until you really, really need them.
If you are sending skins out:
The short term solution is to use a good, inexpensive tannery, because no product lasts forever, but putting good money in to good skins with a good tannery will bring you more years back on your investment then if you 'toss the pelts to the dogs'.
If you are not sending skins out:
Don't use alum, sulfuric acid, or sodium sulfate. This is probably the easiest way to prevent short-term (under 10 yrs. dry hanging) dry rot.
The skins I mentioned and some I have seen in the past are where like old non acid free paper.
Could it be that they where not neutralized enough?
Thanks for your reply
You didn't mention how old they are.
Sounds like acid left in the skin mixed with high humidity.
As - said, any organic substance will rot eventually (I'll probably get an argument from the syn-tan guys) and every commonly used chemical has it's place.
Thorough basification will, without a doubt, minimize that problem and extend the life of the piece.
Good advice on the freezing. You shouldn't have that problem again.