Jeff Lawrence on thu 16 aug 12
Hi
Hiking past old mines yesterday near Telluride, I found a chunk of broken
insulator from a ruined pumping station with what I imagine is Albany Slip
glaze and was intrigued by the hint of opalescence I saw in it.
Anybody studied this glaze enough to know what gives it that glittery
aspect? The Glazemaster analysis reported no phosporus and only slightly
elevated silica.
Pretty darned white body underneath, too.
Jeff
James Freeman on sat 18 aug 12
On Thu, Aug 16, 2012 at 12:24 PM, Jeff Lawrence wrote:
Hiking past old mines yesterday near Telluride, I found a chunk of broken
insulator from a ruined pumping station with what I imagine is Albany Slip
glaze and was intrigued by the hint of opalescence I saw in it.
Jeff...
Melted Albany Slip clay, Ohio Slip clay, Michigan Slip clay, et cetera (all
the same clay, according to Michigan's state geologist with whom I
corresponded several years ago) is just brown, no opalescence that I have
ever seen. What you are seeing is likely what is called "patination", a
process that sometimes occurs due to natural weathering of a glazed or
glass piece that has had long exposure to earth or water, usually through
burial.
The effect is more pronounced on glaze/glass that had a high-ish sodium
content (like original Albany clay), and where the earth is on the alkali
side. The caustic materials in the earth or water slowly attack and
dissolve the glaze or glass, and deposit the dissolved materials, including
silica, in layers on the surface of the object. The opalescence you see,
usually whitish, though sometimes rainbow colored, is caused by the
reflected light being broken up by the layers of deposited materials, much
like the rainbows produced by oil floating on a water puddle.
Your insulator was likely buried for some time, then unearthed by natural
or artificial forces at a later point. I can show you many slip-glazed
insulators that are not opalescent.
All the best.
...James
James Freeman
"Talk sense to a fool, and he calls you foolish."
-Euripides
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