Yup ... last summer I used a clients' old stock Spectrum dense white opal to
bend for replacement lenses for some custom exterior sconces. I did not do
the original lenses. They broke a few and came to me because the original
(cheapo)creator disappeared in the night .... duh!

Anyway, some substance must have leaked onto the glass, and I have no idea
what. I meticulously cleaned the glass prior to firing, as I've fired this
Spectrum white before and know you must be careful. But when I took the
pieces out of the kiln I would find light grey blotches, even patterns, on
the white. No matter how clean I got them, the blotches appeared (with or
without overglaze spray). Under intense lighting I was finally able to see a
very subtle irid surface stain before firing, which in turn became the grey
crud. My only solution was to finally just polish the entire glass surface
on an upright felt wheel with cerium oxide. That worked, and drove the price
through the roof, and I had already made them wait a year because I was busy
skiing Baldy. I could have ordered new replacement glass, but was using the
clients' own old-stock, and in hindsight I would order fresh glass if I ever
encounter this stain again. I've fired a lot of glass, new and old....this
one stumped me (for a while). The client now has better glass lenses than
the originals, because mine slumped nice and even ... the originals were
fuuuunnnnkeeeee.

cheers, Jacques Bordeleau

================================================== ==

"Mike Firth" wrote in message
...
Very strange. Glass should be stored on edge so even leaking water
should
not collect between sheets.
Quality glass should not have a formula that results in alkaline
breakdown.

--
Mike Firth
Furnace Glassblowing Website
http://users.ticnet.com/mikefirth/
"moh3en" wrote in message
oups.com...
hi, during storage of flat glasses they undergo some defects because of
producing some alkaline solutions. can somebody tell me how can I solve
this problem?