Hello Mary,
Many saddles, stirrups and other riding gear have metallic attachments that are made of nickel (dull silver color).  The major corrosion product of nickel is nickel sulphate, which can be dark to bright green.  The sulphur may come from the tanned leather itself or any cleaning/polishing materials.  Fortunately, nickel sulphate is easily removed.  What I have done for my collections in the same situation is cut a small piece of thin, bendable plastic (no sharp edges) and place it between the leather and the metal attachment, so that there is no physical/chemical contact between the metal and the leather.

Prof. Linda Ellis
Senior Curator, University Museum, SFSU
Founding Director [1987-2011], Museum Studies Program
San Francisco State University
Member: New York Academy of Sciences
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From: Museum discussion list [[log in to unmask]] on behalf of David Harvey [[log in to unmask]]
Sent: Tuesday, October 08, 2013 12:08 PM
To: [log in to unmask]
Subject: Re: [MUSEUM-L] Waxy green buildup?

Mary -

Most saddles and tack not only have residues from saddle soap but also oils used as leather dressings over the years. It is common to find a waxy green corrosion product where copper alloys are in contact with leathers and  skin. Organometallic corrosion results from fatty acids, primarily steraic and oleaic acid, which dissolve copper ions from leathers and skins. You also will see this on rings and jewelery that people wear, glasses too, as well as on brass tacks on old leather covered trunks.

Most of the time it comes off easily with swabs moistened with mineral spirits. But it is an inherent condition and will continue as long as the metal and leather are in contact.

A larger issue is all that gunk from the soap and dressings on the leather. Often they are a great food source for fungi (mildew and mold)- so you may see white, black, or orange blooms appear. The organic oils will eventually chemically crosslink and darken the leather, and eventually it may become very brittle.

This is where you need a knowledgeable objects conservator to examine the leather saddle to assess it's condition and make treatment recommendations.

Cheers!
Dave

David Harvey
Senior Conservator & Museum Consultant
Los Angeles CA
www.cityofangelsconservation.weebly.com<http://www.cityofangelsconservation.weebly.com>


On Tue, Oct 8, 2013 at 11:33 AM, Kate McCarthy <[log in to unmask]<mailto:[log in to unmask]>> wrote:
Ok this one's for the conservators and leather goods folks on here. I work at a Western history museum and we are getting a selection of saddles ready for exhibit. However, I've noticed a nasty dark green waxy build up on one of the saddles wherever metal touches leather. This saddle may have been treated with saddle soap at some point and has almost certainly been polished with Renaissance wax at some. The leather does feel sticky to the touch. Does anybody have an idea about a) what is this green waxy build up? B) how do I get this stuff off the metal parts without damaging the leather? C) can I prevent it from coming back?

Thanks y'all!

Mary "Kate" McCarthy
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