Stained glass

Kevin Buschey <kbuchey [at] peoplepc__com> writes

>I am in the process of repairing a stained glass window. ...
>guess it is from the 1920's, possibly a catalogue piece. There a
>number of broken clear pieces of glass. The pieces are framed with
>zinc channels. I am attempting to heat the old solder enough to
>liquify and break bond, so I can disassemble the frame and remove
>the broken glass. The old solder will not liquify when applying the
>soldering iron to it.

My guess would be that because solder is a mix of metals (e.g.
lead-tin), if you look at the phase diagram of the metals involved,
the melting point of the solder is depressed significantly compared
to the melting point of either pure metal. In addition, you get
accelerated corrosion with 2 metals in contact, resulting in one
component of the solder oxidizing and washing out with weathering
and age. This results in a changing ratio of metals in the aging
solder, which results in a changing melting point. This means that
the solder requires ever higher temperatures to melt, potentially by
hundreds of degrees. This explanation here is theoretical, and it
would be best to research further to confirm this.

Valerie Tomlinson
(former conservator, former chemist)


                                  ***
                  Conservation DistList Instance 19:56
                   Distributed: Friday, May 19, 2006
                       Message Id: cdl-19-56-004
                                  ***