View single post by MattKolenda
 Posted: Fri Aug 11th, 2017 05:08 am
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Joined: Wed May 22nd, 2013
Location: Grand Rapids, Michigan USA
Posts: 12

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We use plaster in our mix. 2 parts whiting, 1 part plaster mixed with boiled linseed oil and a dash of black powdered mortar pigment. This is very similar to the recipe you'll find in the SGAA's "Standards and Guidelines for the Preservation of Stained Glass. I very much understand the argument against this practice and used to feel the same way.
I started adding plaster about ten years ago when I read a very compelling article, "Maintaining Stained Glass Windows" in Stained Glass Quarterly by Geoffrey Wallace. He explained how when the plaster is mixed with oil it will repel water rather than absorb it and thus never cure into the hardened form of plaster we might associate with the name. It does render a stiffer panel but is still quite flexible and serviceable.

He also wrote about the procedure of cementing windows in situ and, through capillary action, the cement is able to regenerate itself when new oil or a thin mix of cement is introduced. Since we rarely completely relead a window and only partially relead most of the old windows we encounter, we've had plenty of opportunity to see this first hand both on the bench and in situ. I'm still amazed at the transformation you'll see when you feed thirsty old windows a good helping of oil or thinly mixed cement. The lead and painted glass also seem to appreciate the treatment and shine like new afterward. You don't want to use any whiting during this process and will want to keep the in situ work limited to the exterior. The idea is to leave the cement looking wet with oil. Excess is simply wiped and buffed with rags.

I don't think there will be a day we can ALL agree on a standard mix. We do what works for us. Just don't use Portland or Inland which will render a panel practically disposable.


Last edited on Fri Aug 11th, 2017 05:10 am by MattKolenda

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