Colemanite and spodumene in glazes

[Luca Ask]

Hallo,

Is there anyone who can give me some advice on using colemanite and spodumene in glazes?

I have read that use of colemanite can cause some problem  in glaze if colemanite is present in big concentration (decrepitation). What can be the maximum concentration that give not big problems? 10%?

If my firing is slow is it possible that this problem will be less?

About spodumene:  I have seen that can be better to wash it and that big concentration can determine some "wave" In the glaze. Is this problem bigger in single firing? Someone know why it is better to wash spodumene?

Many thanks

Luca

 

[Hulk]

Hi Luca!

Have read about washing spodumene to remove some of the "soap" that causes bubbling in the glaze. Tony Hansen discusses decrepitation and washing in the links below. Perhaps someone with direct experience will chime in.

I'm using petalite to add some lithium to my lowest expansion clear glaze. It's working well for me; there are some small gray flecks here and there, which may be from the petalite (I'm also using Zircopax in that glaze) - I don't mind them at all.  

Colemanite Colemanite (digitalfire.com)

Spodumene Spodumene (digitalfire.com)

Petalite Petalite (digitalfire.com)

 

[Russ]

Is colemanite still available?

[liambesaw]

1 hour ago, Russ said:

Is colemanite still available?

In Europe, yes

[Dick White]

The processing of the spodumene ore involves using soap as a lubricant in the grinding machines, which leaves a residue on the powdered material. This will cause your glaze slurry to be foamy as you mix it. You can wash it to rinse out the soap and let it dry before using it in your glaze recipe. Or, as I do, calcine it to 8-900℉/450-475℃ to burn off the soap.

 

[liambesaw]

9 minutes ago, Dick White said:

The processing of the spodumene ore involves using soap as a lubricant in the grinding machines, which leaves a residue on the powdered material. This will cause your glaze slurry to be foamy as you mix it. You can wash it to rinse out the soap and let it dry before using it in your glaze recipe. Or, as I do, calcine it to 8-900℉/450-475℃ to burn off the soap.

 

I think it's a surfactant from the float separation process where the ore is ground and then put into large water tanks that bubble air through the ore to cause contaminants to foam at the top which is then scooped off.

 

It's strange though, because this refining technique is used on a lot of the materials we use, the spodumene and lithium just seem to hold onto it really well.

[Luca Ask]

Ok, I tried to wash my spodumene: no foam or bubbles. I immagine that it was already washed before they sell it to me.

[Luca Ask]

It remain the problem with colemanite: my recipe have 15% colemanite and I'm afraid is too much.

Recipes 6 (hoping to have green with chromium ox.)
46,7 Spodumene
5      China clay
14,4 Washed wood ash
14,9 Colemanite
5      Bentonite
14    Quartz

I think my firing is more near to cone 7 than cone 6. I think that I can try to use less colemanite. 

Do you think I can try with 10% and use a little more wood ash?

Or it is better to use only 5-6%?

I'm afraid that with 6% colemanite Boric oxide would be too little.

[liambesaw]

I really think you should try the recipe as is, with the colemanite.  The problems it can cause with expansion are likely going to be counter acted by the high spodumene content.  Spodumene is an extremely low expansion mineral and can cause a glaze to shiver.  The colemanite may be there not just for it's chemical properties but for it's physical properties as well.

I think the decrepitation occurs in glazes high in colemanite, like lowfire glazes.

[Luca Ask]

13 minutes ago, liambesaw said:

I really think you should try the recipe as is, with the colemanite.  The problems it can cause with expansion are likely going to be counter acted by the high spodumene content.  Spodumene is an extremely low expansion mineral and can cause a glaze to shiver.  The colemanite may be there not just for it's chemical properties but for it's physical properties as well.

I think the decrepitation occurs in glazes high in colemanite, like lowfire glazes.

This is a recipe adapted by me: I have not borate frit and I would like to try and use here spodumene. The recipe was for cone 8 and I use it at cone 6-7

The original was someting like this:

Soda feldspar 47

Calcium borate frit 16

Whiting 14

China clay 5

Quartz 18

[liambesaw]

1 minute ago, Luca Ask said:

This is a recipe adapted by me: I have not borate frit and I would like to try and use here spodumene. The recipe was for cone 8 and I use it at cone 6-7

The original was someting like this:

Soda feldspar 47

Calcium borate frit 16

Whiting 14

China clay 5

Quartz 18

Ok, I see then.  I think you may actually have to increase the colemanite in that case if you want similar melting properties.  Soda feldspar has a much lower melting point then spodumene, and calcium borate frit has a whole lot more boron than colemanite. 

The big issue with colemanite is it's high loss on ignition.  It loses 20% of it's weight as gas.  Unfortunately I don't think it can be calcined to fix that like other materials because it decomposes at the same time it melts.

[Luca Ask]

33 minutes ago, liambesaw said:

 Soda feldspar has a much lower melting point then spodumene, and calcium borate frit has a whole lot more boron than colemanite.

I thought it was the opposit!! Good information!

[Min]

3 hours ago, Luca Ask said:

46,7 Spodumene
5      China clay
14,4 Washed wood ash
14,9 Colemanite
5      Bentonite
14    Quartz

 

2 hours ago, Luca Ask said:

The original was someting like this:

Soda feldspar 47

Calcium borate frit 16

Whiting 14

China clay 5

Quartz 18

46.7 spodumene is a heck of a lot of spodumene! Why so much? A 1:1 substitution for a potash or soda feldspar is usually far too much spodumene to use. You want to keep the lithium oxide mole amount to under about 0.2 per mole of total fluxes. Also, do you have an analysis for the calcium borate frit? There are many available ones with differing chemistry, don't know how much boron is in the frit from the original recipe. If you have an analysis for the colemanite you have that would be helpful too.

[Luca Ask]

17 minutes ago, Min said:

 

46.7 spodumene is a heck of a lot of spodumene! Why so much? A 1:1 substitution for a potash or soda feldspar is usually far too much spodumene to use. You want to keep the mole amount to under about 0.2 per mole of total fluxes. Also, do you have an analysis for the calcium borate frit? There are many available ones with differing chemistry, don't know how much boron is in the frit from the original recipe. If you have an analysis for the colemanite you have that would be helpful too.

Ok, this is an experiment, 

I can not know analisis of my colemanite and borate frit of the recipe. I'm going to correct this recipe and the others with linear blend or triaxial probably. Or mixing one with the other.

I would like a recipe with wood ash, high litium and boric oxide for cone 6-7 (without zinc oxide) and I have spodumene, colemanite and lithium carbonate.

That could be the maximum advisable % of spodumene and colemanite in order not to have serious problems? 

 

[Min]

Any soda, potash feldspars or nepheline syenite? 

[Luca Ask]

I dont have calcium borate frit at the moment. I have no type of frit.

The original recipe was from "Colour in glazes" of Linda Bloomfield

Soda feldspar 47 Calcium borate frit 15 Whiting 13 China clay 5 Quartz 17 + 0,5 Chromium oxide (for cone 8). I need for cone 6-7.

I would like to add litium with spodumene.

I have soda feldspar and I can decide for example to use 20-30% soda feldspar with 30-20% spodumene instead of 47% spodumene.

I can use more wood ash in order to have more flux and reduce colemanite if 15% is too much, or use ball clay instead of china clay.

[Min]

Using spodumene instead of the original soda spar is going to throw the silica and alumina amounts off as they differ with those feldspars. Just using hypothetical analysis since I don't know the actual ones for your soda spar and colemanite or the wood ash obviously I'ld start off with something along the lines of this: (just round off to the tenth decimal place) What works in theory doesn't necessarily work in practice so please just mix up a tiny amount of this to try, it will need some altering I'm sure, but should give you somewhere to start. (totals 100)

[liambesaw]

I'd warn against relying on wood ash as a flux at cone 7, it doesn't always perform as one from my own experiments.  I am thinking you're looking for quite a runny rivulet style glaze?

[Luca Ask]

8 hours ago, Min said:

Using spodumene instead of the original soda spar is going to throw the silica and alumina amounts off as they differ with those feldspars. Just using hypothetical analysis since I don't know the actual ones for your soda spar and colemanite or the wood ash obviously I'ld start off with something along the lines of this: (just round off to the tenth decimal place) What works in theory doesn't necessarily work in practice so please just mix up a tiny amount of this to try, it will need some altering I'm sure, but should give you somewhere to start. (totals 100)

Thank you very much! Don't worry, it's right to start, at the moment it's like a game for me.

[Luca Ask]

8 hours ago, liambesaw said:

I'd warn against relying on wood ash as a flux at cone 7, it doesn't always perform as one from my own experiments.  I am thinking you're looking for quite a runny rivulet style glaze?

No, I'm just looking for a normal glaze, trasparent or matt or semi matt.  The important thing is to experiment colours and effects with raw materials and wood ash as flux. It is better for me if the glaze is not runny at the moment.

I will try only 1 runny recipe I think. 

The one that Min gave me.

[Luca Ask]

12 hours ago, Min said:

Using spodumene instead of the original soda spar is going to throw the silica and alumina amounts off as they differ with those feldspars. Just using hypothetical analysis since I don't know the actual ones for your soda spar and colemanite or the wood ash obviously I'ld start off with something along the lines of this: (just round off to the tenth decimal place) What works in theory doesn't necessarily work in practice so please just mix up a tiny amount of this to try, it will need some altering I'm sure, but should give you somewhere to start. (totals 100)

I have tried to play with the glaze calculator. It was new for me!

My proposal is:

24 Spodumene

23 Cornwall stone

18 "Mix" Wood ash

7 Bentonite

5 Ball clay or 10 

15 Silica or 10

8 Colemanite