JJHerb@aol.com on thu 27 mar 97
Monona Rossol wrote "This is why the commercial china industry is very good
about developing surfaces that will resist abrasive cleansers, very hot dish
washers, strongly alkaline soaps (which also can attack glaze surfaces--it
ain't just acids), and so on."
We might note at this point that the solubility of silica (SiO2), our major
high temperature glass former, increases greatly as the pH of an attaching
solution increases. Sodium silicate, water glass, is made by exposing
silicon dioxide (sand) to a solution of (hot, concentrated?) Sodium Hydroxide
(lye) causing the silica to dissolve completely.
In every day life, when the glass surface falls apart the metals contained
are released. When the surface is exposed to acid, the metals can also be
released. Sort of darned if you do, darned if you don t - in the world of
pH. So the answer is to try to keep the glazes as tough as possible with as
little potentially toxic content as possible. Of course, if you re making
Art that no one will lick, do what you like. I have noticed that acid
tongued critics and caustically inclined reviewers never lick any Art at all.
Probably accounts for their survival.
In a related post, I feel that people inclined toward medieval authenticity
in pottery should make such pots and keep them for personal use only. They
(and their children) may then also achieve authentic Medieval life spans.
Strange to have heard from a Medievalist on the net, thought it would have
been on parchment.
Joseph Herbert
JJHerb@aol.com
Ron Roy on fri 28 mar 97
Joseph Herbert wrote -
Of course, if you re making Art that no one will lick, do what you like. I
have noticed that acid tongued critics and caustically inclined reviewers
never lick any Art at all. Probably accounts for their survival.
Seems to me we should make the licking part a requirement.
Ron Roy
Toronto, Canada
Evenings, call 416 439 2621
Fax, 416 438 7849
M Richens on sat 29 mar 97
In article <970326145655_-1437503884@emout09.mail.aol.com>,
JJHerb@aol.com writes
>----------------------------Original message----------------------------
>Monona Rossol wrote "This is why the commercial china industry is very good
>about developing surfaces that will resist abrasive cleansers, very hot dish
>washers, strongly alkaline soaps (which also can attack glaze surfaces--it
>ain't just acids), and so on."
>
>We might note at this point that the solubility of silica (SiO2), our major
>high temperature glass former, increases greatly as the pH of an attaching
>solution increases. Sodium silicate, water glass, is made by exposing
>silicon dioxide (sand) to a solution of (hot, concentrated?) Sodium Hydroxide
>(lye) causing the silica to dissolve completely.
>Joseph Herbert
>JJHerb@aol.com
Hi,
This is talking about Silica. _BUT_ if we are talking about glasses and
glazes the attack mechanisms vary greatly depending on the pH and
strength of the attacking medium. One of the WorsT is pure distilled
water at boiling point.
Acid solutions (ignore HF for the moment) attack the fluxes in the glass
dissolving them and opening up the silica skeleton so you get a dull
finish where attack takes place. (used for producing pure Vitreous
silica sheaths for heavy duty heaters)
The strength of the acid is critical. With boiling Sulphuric Acid
solutions the attack increases up to 25% and the drops to not a lot at
full strength because the acid is no longer ionic.
Culinary acids such as Citric can be worse than sulphuric or
hydrochloric as they will chelate with the metals present and make them
into soluble complexes. That is why comments about orange juice and
metal release are important.
Alkalis attack the silica skeleton. Other additions such as Zircon can
inhibit this attack in a way that Alumina won't.
(Molten NaOH eats glass and at a slower rate a 50% solution at boiling.
Doesn't touch stainless steel though.)
Pure water tends to cycle between the two states and thus expose more
fresh surface to attack.
There was an excellent paper several years ago on this but I can't
remember if it was the J Am Ceram Soc or not. Sorry!
( no cents so will 2p british do?)
Max
--
Max Richens max@richens.demon.co.uk
+44 (0) 1925756241
Enamel Consultant - Ceramist - Analyst programmer
Software for Batch Formulation and Millroom control.
Tony Hansen on sun 30 mar 97
I don't suppose you'd like to turn that post on Clayart about solubility
into an article to post on the web for permanent reference of
everyone. We'd credit it to you and maintain it for you.
Would you like to distribute demo copies of your software on our site.
I'd be happy to have a look at it and give you a home page no charge.
What do we want? Nothing but some good articles!
--
=================================================================
Tony Hansen, IMC - Get INSIGHT 5 beta or The Magic of Fire II at
http://digitalfire.com or http://www.ceramicsoftware.com
| |
|
