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Post by sundancerdori on Jun 18, 2016 21:07:28 GMT -6
Although I am quite new to crystal glazing, I’ve encountered an issue with the coloring oxides and hope that those of you with more expertise can answer it. I am using 2 different glazes, firing at C6 ox, Fa’s #5 Rvsd, and MFE. I’ve listed the recipes below along with 2 pics from a recent firing. My question is: when I use 2 coloring oxides to get different colors between the crystal and ground/field, like Manganese and cobalt oxide for Purple crystals on a tan ground, all I end up with is “the Blues” – Blue crystals on blue ground, not “Purple on Tan” (with the Fa’s glaze). Same thing with the MFE glaze - I added Cob carb and Copper carb for a Blue Crystal on Green ground, but again all I got was Blue crystals on blue ground (see pics below). I know from quite a bit of reading that certain oxides have greater “strength” than others, but these color variations are commonly listed in recipes, so why am I not getting the color separation? Why do I just get the Blues?
“Purple on Tan” Fa's #5 Rvsd (Purple Crystal, Tan Ground)
F3110 50
Zinc 27
Silica 14
Talc 5
Spodumene 4
Titanium 2 Cob. Carb 2
Mang diox 1
Bento. 2
“Blue on Green” MFE Base (Blue Cryst., Green Ground)
3110 50
Zinc 23
Silica 22
Lithium 3
Titanium 1
+ Cobalt carb 1
Copper carb 1
Thank you for any help you can offer, Dori
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Post by evan cornish-keefe on Jun 19, 2016 23:51:25 GMT -6
Cobalt is a strong colorant and can overpower other colorants, adding .1% cobalt carb can give a noticeable blue and I usually find it's color too strong at 1%.
Manganese dioxide on the other hand i find gives a quite subtle color at 2%, generally.
For blue on green i'd try around .5% Copper carb, .2% Cobalt carb, and i'd leave out the Titanium.
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Post by Avi on Jun 20, 2016 15:05:13 GMT -6
Yep, try leaving out the Titanium!!
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Post by mariewright on Jun 20, 2016 19:40:25 GMT -6
Hi Dori,
For the purple and tan - I use 0.2 cobalt, and 2 manganese. I would take the titanium out, but I would also try it with 1 and 2% titanium. I find that adding a little titanium can really improve my crystal shapes. My purple on tan has 1% titanium, but who knows how it will work with your base glaze?
For the blue on green, try a mix of nickel and copper with no titanium. I don't remember what ratios I used for this, but you could try 1:3, 2:2, and 3:1 and see what that gets you. Once you get what you like, you can add in maybe 1 or 2% titanium and see what happens.
Good luck,
Marie
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Post by sundancerdori on Jun 21, 2016 10:03:56 GMT -6
Thank you Marie, Avi and Evan, for your suggestions, but I'm curious to know a bit more about the role of titanium in crystal glaze recipes. If I'm not mistaken, I think I've read that it helps to promote crystal growth(?) and can act as an opacifier in some glazes, but what is the reason for leaving it out? Does the titanium have a down-side, like interfering with developing certain colors?
Given the fact that my first glaze pic above (Fa's) had NO problem developing crystals, I don't think it's a problem to leave it out, but the MFE recipe didn't develop nearly as many crystals, so will leaving the titanium out reduce the # of crystals even further? I realize that I can increase the zinc in the MFE to help develop more crystals, and reduce it in the Fa's to get less crystals, but I was under the perhaps mistaken impression that titanium played some sort of role in developing the crystals, especially at C6. If anyone can add to my understanding of titanium in crystal glazes, I sure would appreciate it. In the meantime, I'm off to prep some more glaze.
And just an fyi, this was just my 3rd attempt at crystal glazes, in a new kiln, which had some sort of power-failure which I had to then re-fire... Well, with that kind of trifecta you can probably understand that the fact that I had ANY crystals at all was quite exciting to a Baby Crystallieri like myself. ;*)
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Post by adammacmillan on Jun 22, 2016 8:26:06 GMT -6
Hi Dori,
Jumping in here...titanium will act as an opacifier (which will subsequently change colors of the glaze), crystal shape modifier, and tends to increase the growth rate of the crystals. Yes, Ti will interfere with certain colors. For example, when doing blue crystals on a yellow background (using 1-2% Nickel), if you add more than about 3% Ti, you will get green on greenish yellow, or as i call it...hot dog relish.
The crystal ratio can depend on many things, including glaze thickness, firing temp, body, and location in your kiln if it isnt super even firing. The titanium may have had somewhat of a role, but looking at your formulas the most obvious thing is you have 4% more zinc in the purple on tan. Just based on the color aspect alone, i would modify your formulas below like so and give them a shot.
Purple on Tan
F3110 50
Zinc 25
Silica 14
Talc 5
Spodumene 4
Titanium 6
Cob. Carb .1
Mang diox 1
Bento. 2
Blue on Green
3110 50
Zinc 25
Silica 22
Lithium 3
Titanium 3
+ Cobalt carb 0.25
Copper carb 2
Good luck!
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