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Chemical Resistant Glazes


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#1 Round2potter

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Posted 02 December 2012 - 07:42 PM

A teacher at my college said something that really struck a chord:
"As potters it is our responsibility to ensure that our products (on the subject of food safe glazes) are of the highest possible quality" -Careen Stoll

In the quest for super durable, ultra food safe glazes for use on dinner ware, i am trying to make my liner glaze better.I have recently been doing a ton of research on glass and ceramic glazes, and have run across some interesting properties of different (common) oxides added to glasses and ceramic glazes.

The effect of Titania (TiO2, also known as the mineral Rutile), typically added to glass as a pure calcined powder, increases the glasses resistance to chemical and physical attack (acids included).

As we are all probably aware, Titania also has good opacifying powers, this also gives it the added benifit of imparting UV/UVA/UVB/UVC blocking powers (it actually stops most forms of light, including the visible spectrum, that's why a clear glazer turns white).

So, THE QUESTION IS:

Has anybody on here that does simple vinegar/lemon acid tests or real lab tests of their glazes tested the effect of Titania?
Has anybody seen ceramic specific information on it?
Anybody ever put a Titania glaze in the microwave?

There are other metals used for this same purpose, but in light of recent talk of Ag and Au, lets leave out the RARE or EXPENSIVE additives this time!

Looking forward to hear All of your experiences
"There is no such thing as cheating in clay; So long as it works"

#2 Round2potter

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Posted 03 December 2012 - 01:44 AM

Can anybody with a fancy glaze program tell me if this would melt at ^10?

In %
74 SiO2, 13 Na2O, 10.5 CaO, 1.3 Al2O3, 0.3 K2O, 0.2 SO3, 0.2 MgO, 0.01 TiO2, 0.04 Fe2O3
"There is no such thing as cheating in clay; So long as it works"

#3 Marcia Selsor

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Posted 03 December 2012 - 09:45 AM

Your numbers look a bit strange.

Somewhat related to limit formulas and then %. Just at a glance I'd say you are too high in Silica.
Limit formulas for cone 8-12 are:

RO radical R2O3 Radical RO2 Radical
KNaO .2-.4 Al2O3 .3-.5 SiO 3-5
CaO .4-.7 B2O3 .1-.3
MgO 0-.35
ZnO 0-.3
BaO 0.-.3

What kind of glaze formation are you using?

Marcia

#4 Round2potter

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Posted 03 December 2012 - 06:38 PM

Tell ya the truth that was a formula i found for the soda lime glass used in commercial food storage containers like mason jars etc.

This recipe uses the addition of Ti for chemical resistance. From what i can tell there is so little of it represented here i would bet it'd be included in basically any Feldspar same for the Fe,

I think i am going to whip up a quick batch from this and see what it will do. probably throw it in a bowl or scrap cup or something for the sake of my shelves.

Thanks Marcia for the temp info. Sounds close enough for me, if it dont work ill just throw in some pearl ash or a little soda ash till it melts.

-Burte
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#5 Marcia Selsor

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Posted 03 December 2012 - 08:24 PM

Burte,

So are you taking a glass recipe and trying to make it a glaze?I think glass with a sodium base melts around 1700 or 1800 degrees. When I was blowing glass in grad school , that seemed to be the melting point. for as much as I can remember about it after 40+ years.
Cone 10 is a bit hotter at 2300.
Lead crystal may melt at the same temperature as the soda glass, but it eliminates bubbles maybe because it is a purer source of flux.. 7-up bottles were sodium base glass, green and full of impurities .Also soft sodium glass etches ...as antique soda glass gets irridescent so I am not sure why you think it is chemical resistant? The lime may do it because calcium does harden glaze surfaces.
But most glaze recipes I have used at contained 10, 20 maybe 30% silica at the most.
Another thing to consider is the coefficient of expansion and contraction. ..something not of concern for melting glass
and not dealing with a fit wrapped around clay.

Marcia

#6 Round2potter

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Posted 04 December 2012 - 12:15 AM

I am more or less using this recipe as a guideline for inert glass.
As for the glaze fit, i figured i would cross that barrier when it comes to it.

As for calcium, in the glass matrix calcium is the most readily dissolved silicate, this is the main cause of soda lime glass deteriorating over time; although i dont know about it's effect on hardness.....

I see this recipe and i see (in regards to my temp range) a sodaspar base glaze with a lil Ti and some Wollastonite for Ca, And depending on the applicability of it, a TINY bit of epsom salt would help and provide the Mg.
Plus flint or ball clay.
"There is no such thing as cheating in clay; So long as it works"




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