A discussion by Jonathan Kaplan on dealing the with fickle nature of this glaze
The following is a submission from Jonathan Kaplan email@example.com to the Clayart discussion group on the Internet.
I've been a participant on this list for probably 5 years or so, and it amazes me that for this length of time, there are many re-occurring topics, not to mention perhaps the most popular one, "RE: Floating Blue." And of course, there are many others, too numerous to mention, but its the nature of the list, and that's OK. But I am troubled with the threads on "Floating Blue" and I'll tell you why.
Seems to me that this is a fickle glaze, to say the least, fires in the neighborhood of cone 6 oxidation and when it works, gives a blue with some interesting surface activity, sometimes called a "reactive" glaze. Also,it's apparent to me that this glaze gives a reduction type surface in an electric kiln, which we all really know fires in a neutral atmosphere. What is most obvious to me in reflecting back on years of this post, including some of Ron's adjustments that when it works, it works fine, which is not very often, and when it doesn't work, it has been called many nasty things, one of the most recent calling it snot green. Whatever. And my sense is that it doesn't work most of the time at least in the comments that I have read on the list. So I am prompted to ask why are you struggling with this glaze, loosing pots over and over in a valiant struggle to obtain this surface? Sure I know that many are not able to have a gas kiln, and that's fine. But to continue to butt heads with this glaze seems to me counter productive, to say the least. So what to do? I'm hearing it now, "God, I really want that funky runny surface active glaze with lots going on in my electric kiln but this Floating Blue is driving me nuts." "And here's Jonathan putting in his 2 cents." Or something like that.
Let me propose the following suggestions. I preface this by including here that as a custom production shop for the ceramics industry including the pottery, giftware, tabletop, etc. segments of this field, we work throughout the temperature spectrum and in any atmosphere. Let me postulate that a surface reminiscent of "Floating Blue" is very obtainable without the struggle of using "Floating Blue" at mid range temperatures in an electric kiln. We do it weekly for clients. While I am not at liberty to post formulas that would violate my non disclosure agreements with my clients, here are some ways to achieve this "elusive" surface.
1. Layering glazes. To develop surface depth and activity, layer glazes either by dipping, pouring, or spraying. Of course, you have run many tests before committing a large body of work, haven't you?
2. Use a slip glaze underneath your glaze to develop a breaking surface, or use a slip glaze over your glaze. We have used a glaze that is mostly Barnard slip with some additions over a one of our glazes to produce a fabulous variegated surface with incredible depth (and yes, blue or blue grey/green) at cone 4 in the electric kilns.
3. Combine two glazes in a line blend. Trust me, some of our most successful surfaces have resulted from this simple task.
4. Use commercial glazes for your temperature range over your shop glazes for either a full coating or for decoration.
5. Diversify the fluxes in your formula. We use several base glazes at cone 5-6 that contain Fusion frits as well as spars.
6. Take a glaze that fires at a higher temperature and re-calculate it to fire at your temperature.
7. Combine some or all of the above suggestions, and of course, test test test.
8. And finally, eliminate "Floating Blue" as you may know it, from your glaze repertoire, and concentrate on not trying to duplicate the reduction look in an electric kiln. Use and exploit the electric kiln for its virtues and incredible firing abilities.
To expand somewhat on Mr. Kaplans comments we could offer the following pointers:
When glazes crystallize as they solidify variegated fired surfaces result. Fluid glazes with plenty of coloring oxide (i.e. iron, cobalt, copper) and TiO2 (especially form rutile) tend to grow crystals as they cool. The slower you fire the better the effect will be. The lower the alumina the better it will be. However note that low alumina glazes tend to run excessively and have low clay content which can give them poor application properties (settling, dusting, uneven coverage).
You can create variegation by splatter-spraying a second layer of glaze with a contrasting color. Use a trigger or pump operated garden sprayer to achieve the effect. Experiment using a more and less fluid overlay.
Double layer glazing works better when the lower layer is more fluid. The upper, stiffer layer tends to break into islands revealing rivulets of the lower glaze. Color the layers to achieve the desired effect. Be aware of the problems associated with double layer glazing (cracking and crawling when either layer has too much shrinkage or is applied too thick or onto wet ware).
Variegation can take the form of variations in the opacity and depth of a glaze. Often the same glaze can have dramatically different appearances at different thickness. You can exploit this by applying the glaze to an incised or roughened surface. The glaze stretches into a thinner layer on the edges of imperfections and contours thus creating variegation.
Simple additions of lithium will often produce variegated fired surfaces. Infact you might consider adding up to 30% Spodumene (a source of Li2O) to a cone 6 glaze. Augmenting this with high magnesia (i.e. 0.4 equivalent from talc or dolomite) and rutile will produce silky mattes similar to cone 10 reduction effects. Use boron to melt the glaze more if needed.
Additions of tin-rutile mixtures will variegate almost any glaze.
Additions of magnesium carbonate, a very refractory powder, will give a glaze texture and even make it crawl in interesting ways. Some glazes use up to 50%.
MgO can help matte a glaze at cone 6 (as it does at cone 10). Use dolomite and talc to source as much as possible yet still achieve a good melt.
Additions of manganese granular (or any granular metal oxide) to a glaze will give it a more interesting surface. Look for the lightest possible particulate to minimize settling out or use a body with added granular colorant.
Variegation is far better controlled if you understand the mechanism of the variegation (i.e. is crystal development, variation in thickness, non-homogenous melt) and if you know something about glaze chemistry. Looking at a glaze at the oxide level and rationalizing its fired behavior on this level gives you the ability to fine-tune the mechanism and either enhance it or make it more stable. In addition you can appraise other glaze properties like thermal expansion, hardness, solubility to acids, color, clarity and depth, susceptibility to pinholing/crawling, etc. Our INSIGHT software will help you work on the oxide level.