Preserve crazing of 3110 based glaze but lower melting temp

[mr_glazy_man]

Hi all,

I'm trying to create a beautiful, transparent crackle glaze.

My first thought was a high sodium frit – 3110. Doing a bit of research on Digital Fire suggests that 3110 is a very low melting frit. I combined it with 10% EPK (the classic 90% frit, 10% clay combo) and test fire across these temperatures at five temperature points between 935C - 1110C. 

I couldn't get it to nicely melt until it hit 1080; any lower was extremely underfired. Moreover, punching this into the Glazy calc does indeed suggest that it is *almost* underfired. 

I want to get this glaze to melt glossy at around 05. My instinct is to pair it with 3195 for the melting power of higher Boron, but 3195 is also a higher (relatively speaking) magnesium frit and will likely reverse the crazing via COE alteration.  My next thought was to add the 3195, but also add some Neph Sye for the sodium. 

Any thoughts on how you might tackle this? 

 

 

[Callie Beller Diesel]

Before assuming that the magnesium in 3195 will eliminate your crazing, try it and see. Remember that the clay body will play a role in it as well, and there are lots of clay bodies in my neck of the woods that will glazes will craze on with the use of that frit.

I don’t know if food durability is a concern with this glaze, but both of the versions you’ve posted have an unbalanced flux mix. They will likely be soft, and may etch easily. 

[Min]

6 hours ago, mr_glazy_man said:

I want to get this glaze to melt glossy at around 05. My instinct is to pair it with 3195 for the melting power of higher Boron, but 3195 is also a higher (relatively speaking) magnesium frit and will likely reverse the crazing via COE alteration.

Ferro frit 3195 does't contain magnesium. It contains SiO2, Al2O3, B2O3, CaO, and Na2O.  Ferro frit 3249 is a good one to supply magnesium if that's what you are looking for. 

Are you looking for a crazed / crackle  ^05 glaze for non functional work? 

[mr_glazy_man]

Thanks for the answers team. 
@Min Yes, I’m looking for a nice crazed finish for tile at 05. Doesn’t need to be food safe.   And you’re right, 3195 doesn’t contain magnesium at all - don’t know where I got that idea from…I got the composition mixed up with 3249 for Pete’s sake evidently. 

@Callie Beller Diesel is it the R2O:RO that you’re worried about? I’m reading that it should probably be closer to .2-.3:.7-.8? I suppose the reason it’s so out of whack is because I’m aiming for high Na2O to help induce crazing, but my efforts may be misdirected in this sense

Edited November 2, 2022 by mr_glazy_man

[Min]

15 hours ago, mr_glazy_man said:

Doing a bit of research on Digital Fire suggests that 3110 is a very low melting frit. I combined it with 10% EPK (the classic 90% frit, 10% clay combo) and test fire across these temperatures at five temperature points between 935C - 1110C. 

I couldn't get it to nicely melt until it hit 1080; any lower was extremely underfired. Moreover, punching this into the Glazy calc does indeed suggest that it is *almost* underfired. 

Can't take any frit and add 10% epk and expect it to work. 

Have a look at boron levels in the unity formula, need to have the boron for a ^05 - 04 glaze at least around 0.50 to melt properly. 90 ferro frit 3110 + 10 epk will give you a boron level of 0.10 (unity formula using Insight glaze calc). This is low even for a cone 6 glaze, let alone a lowfire one.

Work on getting the boron up to the 0.50 range. If you go really far above this you will likely get boron clouding, this might not be an issue, depends if you want a clear crackle/crazed glaze.  I'ld suggest trying ferro frit 3195 + ferro frit 3110 + epk + dolomite (if you have it, talc if not). Play around with those 4 materials on Glazy, you should be able to get 4 points covered: adequate boron levels, adequate silica and alumina, flux ratio at the 0.3:0.7 ratio  plus a high expansion to cause the crazing.

Edited November 3, 2022 by Min
decimal points

[mr_glazy_man]

@Min Why do you recommend the Dolomite? 3249, a magnesium frit, is usually chosen to counteract crazing by reducing expansion. Won’t dolomite do the same, since it’s a magnesium source?

I get your point about the boron levels though. Wish I had just thrown it into the calculator before testing it.  

[Min]

I suggested some magnesium to get the flux ratio into a good range, could use calcium instead. Yes, fritted form of magnesium would enter the melt easier than dolomite or talc but magnesium frits are super expensive, at least where I live. The amount you need shouldn't be much, can still have a high expansion crazed / crackle glaze with a little magnesium in the recipe. If you can make a balanced recipe using all frits plus a bit of clay to keep things somewhat suspended that would melt the best. If you don't have access to the COE figures on Glazy then post your potential recipe(s) here and I'll run them through Insight for you. Keep the sodium and potassium high.

[mr_glazy_man]

Great! These are my two contenders. It's hard to get the boron level up without sacrificing Na2O. And then, if you introduce too much Na2O, the R2O:RO is out of whack. It's a real balancing act.

Let me know if you have any thoughts

[Min]

I'ld suggest getting the boron up to 0.50 

Calcium carb and dolomite are not the greatest fluxes for lowfire so it's going to take more boron than you have to get a good melt. I don't know what the application of the tiles will be, if you can sacrifice some durability the flux ratio doesn't have to be in the 0.3:0.7 range.

[mr_glazy_man]

@Min just came up with this. Had to sacrifice durability to get to .5 Boron , but Stull is telling me it’s not in the crazing range. I suspect it probably still will. What do you think?

I have the above two “Crazing 02 and 03” coming out of the kiln tomorrow. Ill post the results.

Edited November 4, 2022 by mr_glazy_man

[Min]

If the glaze doesn't need to be durable it opens up a lot of possibilities, even using a raku crackle glaze. Thing with Stull charts and crazing it doesn't take into account different claybodies or firing cone. Looking forward to seeing your results.

If you have ferro 3134 you could use that to supply boron with the 3110 and 3195. I did a quick example one below, if it's too runny you should be able to add up to 5 more epk and still have a good crackle / craze.

Flux ratio is 0.4:0.6 LOI is only 1.0 so it should have very little micro-bubbles and be very clear. Could be really runny so if you test it fire on a waster. 

Something like this

 

Edited November 4, 2022 by Min

[mr_glazy_man]

I’ll absolutely give this a go. Thank you @Min I’ll also post my results in a couple of hours once they’re out of the kiln. 

The concept of “durability” is interesting to me - what aspects of durability are we talking about? Is it mostly related to food safety? Therefore, cutlery marking? Leachability? Or is it more about strength, dent resistance etc?

I’m making wall tile, so the type of durability I need is abrasion and impact resistance. It’s not functional in the sense that we’re eating off them, but it’s still a functional item per se. I suspect my perspective is coloured by the fact that I… am not actually a potter, so my definition of durability may be different to yours

[Min]

2 hours ago, mr_glazy_man said:

The concept of “durability” is interesting to me - what aspects of durability are we talking about? Is it mostly related to food safety? Therefore, cutlery marking? Leachability? Or is it more about strength, dent resistance etc?

Durable glazes are those that can withstand abrasion from cutlery without scratching or marking and resist chemical attack. I haven't read about dent resistance of glazes but many people prefer glazes not to craze for functional ware.

I'm thinking that as far as your wall tiles go (good to know what you are making), the tile and glaze would break together with a heavy impact. I would imagine your abrasion resistance would be along the lines of what potters making functional ware would test for with cutlery.  To increase the durability of a glaze having as much silica and alumina in the glaze as can be taken into a melt is important as is firing the glaze to maturity and not overloading the fluxes or colourants. Flux ratio might or might not make a difference for your purposes. I would do lots of testing of the glazes in the manner in which you would expect the tiles to be used. Cleaners used, brillo pads  etc.

[mr_glazy_man]

I have conducted these tests. Two samples, each fired at 1040 and 1080deg Celsius. 

I mixed 6% copper oxide  to give it colour as the clear was very difficult to read. 

What’s interesting is how both the Wollastonite and Dolomite seems to have opacified what should be a transparent glaze. @Min I think you’re right on the money here - the boron isn’t low enough to melt both of those. I have another test in for 1120deg, so we’ll see if that makes a difference. I will now be trying @Min recipe of 3195, 3134 and 3110.

Tangentially: does Wollastonite typically opacify a glaze? I’ve seen this with another glaze I’m testing - what should be a dark black matte finish comes out a grey. 

[Min]

4 hours ago, mr_glazy_man said:

the boron isn’t low enough to melt both of those

I think you had a typo here, boron isn’t high enough.

4 hours ago, mr_glazy_man said:

Tangentially: does Wollastonite typically opacify a glaze?

Wollastonite melts more than whiting + silica but fritted calcium melts better than both.

5% copper oxide is a heck of a lot, do you need that much to get the colour you want? I would suggest trying base glazes without colourants as well as with as the colourants can change glaze behaviour.