pdp1@EARTHLINK.NET on sun 25 apr 04
Glasswares...
Hi Tom,
Happy Spring!
My understanding -
We do well to not leave liquid things in 'glasses' for
extended periods...
That's all...pretty easy to do...or not do. Let things be in
them only briefly, as it were.
'Crystal' or other glass Liquor decanters for example,
however charming, provide prolonged liesures for leaching to
occur. Not so good.
(...as for the products we buy as come in Glass containers?
where liesure, to some degree has been theirs? Hmmmmm...?
Maybe not so good sometimes too...)
The whole matter of 'Leaching' generally, seems unerringly
so far, to neglect, that there is a requisite time-element
for something to leach.
I owe my appreciation in this to Ron Roy's enlightening
reminders some years ago, when I was roused from my blind
faith of 'glass'...and likewise, as regard Pottery in
general as is hi-fire...my having imagined previously, that
it were all resistant to leaching.
So now, I am a gentle, minor apostle, wandering the lands
with the word...or at least pipeing up now and then.
Love,
Phil
el ve
----- Original Message -----
From: "Tom Sawyer"
> If glass artist have the same problems with leaching -
perhaps even more as
> you suggest, this begs the question if we should be
concerned about leaching
> of various chemicals from the glasses we use about the
home. As I stated in
> my earlier post, I don't ever remember colored glazes that
I purchased
> changing color or showing signs of leaching; admittedly, I
didn't look. I
> remember many years ago buying a bunch of glasses in
Mexico and then finding
> the same in Pier One and replacing broken ones; they are
all gone now but I
> do wonder what third world artist might use and whether
such items are safe.
>
> Tom Sawyer
> tsawyer@cfl.rr.com
>
> -----Original Message-----
> From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf
Of Ivor and Olive
> Lewis
> Sent: Wednesday, April 21, 2004 2:50 AM
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: Re: Leaching
>
> Dear Tom Sawyer,
> The majority of glass products are based on Silicon
Dioxide which, because
> of its high melting point has to be fluxed. Common fluxes
are Na2O, K2O and
> PbO, augmented by CaO, MgO and ZnO to give chemical
stability. Al2O3 is
> added to suppress devitrification and increase viscosity.
> Over time, glass buried in the earth begins to decompose
under the influence
> of wet acid conditions and when dried is found to have a
form of optical
> lustre which gives an iridescence. I think this is due to
the leaching of
> the Alkali Metal ions.
> Charles Bray, "Dictionary of Glass. Materials and
Techniques" ISBN
> 976-6910-89-5. 1995, tells us that Na+ and K+ ions are
very mobile and can
> be leached with water.
> Such information leads me to believe that our Ceramic
Glazes, which contain
> high proportions of Alumina as well as Alkali Earth
elements and are usually
> low in Alkali metal elements would have a greater degree
of chemical
> stability than most of the glass used by Glass Artists.
> Perhaps someone else could find confirmation of my opinion
in the ACerS
> archives.
> Best regards,
> Ivor Lewis. Redhill, South Australia
>
>
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