Modification Date: 2019-10-03 11:13:07
|Fusion Frit F-524||850.0||82.9%|
|Fusion Frit F-69||40.0||3.9%|
I developed this for cone 04 to fit as many clay bodies (without crazing) as possible (my Zero3 clear works well on specific bodies but does not melt enough at cone 04 and it's thermal expansion is too high to fit some bodies). I am developing a recipe for a terracotta casting body at the same time as this and I am working to make it compatible also.
I found the inspiration for this on testing many commercial clears and finding one that stood above the others regarding fit and clarity at 04. I have always been under the impression that low fire bodies have a wide enough range of thermal expansions that one glaze cannot be expected to fit them all. And that if a glaze melts well at cone 04 it will have too much melt fluidity past cone 02. But this glaze has made me question both, I am shocked at how it is possible that it can fit so many bodies and work across such a wide temperature range. In fact, I have not found a body that it does not fit! So I had it analyzed at a lab and then created a recipe to source its chemistry. A stroke-of-luck was that a frit we already use to produce another glaze, Fusion Frit F-524, is close to the complete chemistry needed.
I have been surprised by other aspects of this recipe. It is crystal-clear on any body at any thickness (at cone 04 and above)! Additions of tin and zircon produce a white that melts just as well as the clear. It is amazing how the mobile the melt is, how it runs right off my fluidity checker! Yet it is not significent more mobile at cone 1 than cone 04. There is some kind of magic with this chemistry that I am anxious to learn more about.
While it hardens to a powdery surface, it is amazing how little gum solution is required to make it dry hard and hang on to the bisque when other layers are added on top.
For the first mix I added 3000g of powder to 2400g of water to produce a specific gravity of 1.48SG. This produced a watery slurry. I added epsom salts to the point where further additions did not thicken the slurry (up to a total of 7g). This improved it considerably but it was still a little thin (although it covered and applied like a typical dipping glaze, drying in seconds on bisque ware). However the surface was too powdery so I removed 400g of water and replaced it with 400g gum solution. This slowed dip time to about a minute (waiting for the dripping to stop) but it now tolerates thick overlaying of Majolica colors (without them pulling it away from the bisque). For a single-coat dipping (where no overglaze work will be done) I would use about half the amount of gum solution.
SIAL bodies are made in Montreal, Canada. The glaze was applied by dipping. The fit is still holding on both bodies after many months.
The commercial cone 04 clear brushing glaze on the left works really well on our bodies so I sent it away to be analyzed (about $130). From that information and using my account at insight-live.com I was able to create a recipe, having the same chemistry, employing two Fusion frits (which amazingly supplied all of the fluxing oxides). In this amazing cone 04 melt fluidity comparison they are almost identical (mine, G3879, has a little more surface tension). The Al2O3 and SiO2 levels would make, even a cone 6 glaze, jealous! So it should be very durable. And it has low thermal expansion (no crazing). With the bucket of dipping-slurry I made I can glaze a piece perfectly evenly in seconds rather than the normal 10 minutes of fiddling with a brush and three coats! I have used it on dozens of pieces, it's amazing. I can't wait to start adding stains!
Look at how fluid G3879 is at cone 06 even though it has the Al2O3 and SiO2 of a cone 6 (or even cone 10 glaze)! It have found that glazes with lots of boron can tolerate amazingly high levels of Al2O3 and SiO2 and still melt very well. And they create many options to lower thermal expansion that would not otherwise be available. The G3806N recipe has the amazing ability to tolerate large additions of kaolin. Each addition sacrifices some melt fluidity but the glaze stays glossy and gets more durable (because of the increased Al2O3 and SiO2). And the thermal expansion drops even more. A highly melt fluid, super gloss with low thermal expansion is super difficult at cone 6, but here it is. The secret is high boron. From frits.
Look at how translucent this is! I can fire one of these in three hours, cold-to-cold. I am casting them with molds made using the 3D-printing process. Anyone could do this. Incredibly exciting. And with the G3879 glaze it looks awesome, just like bone china. Notwithstanding this, the Zero3 recipe has to be altered for casting. Initially I have reduced the VeeGum to 1% but it is still casting too slow. And it is not shrinking enough to pull away from the mold well. I am considering strategies on how to increase drying shrinkage and am going to add more frit to take it down to cone 04.
Notice the water has wicked up to about 1 cm from the rim (the piece sat in water overnight). The glaze fits so there are no cracks for the water to seep through. However, being fired at cone 04, the body is quite porous. The piece has a unglazed base. Notice the water even travelled up the handle. Less exposed bare clay on the base would improve the situation somewhat, however it would be much better to choose a body that vitrifies sufficiently dense so that it does not absorb water (or fire to a higher temperature). There is a not-so-obvious issue here also: Although this piece did not explode in the microwave, it got incredibly hot. Amazingly, through all of this, the glaze has not crazed. It is G3879.
In Bound Links
The term "Zero3" was coined by Tony Hansen. It refers to recipes he developed at Plainsman Clays that enable a potter to create red burning stoneware and blue-white porcelain at cone 03 (links to recipes at the bottom of this page). He arrived at cone 03 after a long testing program that attempted t...
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<recipe name="Cone 04 Transparent Low-Expansion Base Glaze" keywords="A super transparent low fire base clear glaze created by reverse engineering a commercial product." id="141" date="2019-09-05" codenum="G3879">
<recipeline material="Fusion Frit F-524" amount="850.000" added="0"/>
<recipeline material="Fusion Frit F-69" amount="40.000" added="0"/>
<recipeline material="EPK" amount="90.000" added="0"/>
<recipeline material="Silica" amount="45.000" added="0"/>
<url url="https://digitalfire.com/4sight/recipes/cone_04_transparent_low-expansion_base_glaze_141.html" descrip="Recipe page at digitalfire.com"/>
By Tony Hansen