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G3879 - Cone 04 Transparent Low-Expansion Base Glaze

Modified: 2019-09-05 13:20:49

A super transparent low fire base clear glaze created by reverse engineering a commercial product.

Material Amount Percent
Fusion Frit F-524*85.0082.9
Fusion Frit F-69*4.003.9
EPK*9.008.8
Silica*4.504.4
102.50

Reverse-engineer a commercial transparent glaze to get the recipe

Reverse-engineer a commercial transparent glaze to get the recipe

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!

SIAL 10F and 25F with G3879 clear glaze at cone 04

SIAL 10F and 25F with G3879 clear glaze at cone 04

SIAL bodies are made in Montreal, Canada. The glaze was applied by dipping. The fit is still holding on both bodies after many months.

This mug has waterlogged because it is not vitrified

This mug has waterlogged because it is not vitrified

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.

Casting Zero3 Porcelain

Casting Zero3 Porcelain

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.

Low fire glaze with the Al2O3 and SiO2 of a cone 6 glaze

Low fire glaze with the Al2O3 and SiO2 of a cone 6 glaze

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.

Why do these cone 04 and 6 clear glazes have so similar a chemistry?

Why do these cone 04 and 6 clear glazes have so similar a chemistry?

The glaze on the left (as shown in my account at insight-live.com) is a crystal clear at cone 04. The high frit content minimizes micro-bubbles. The high B2O3 melts it very well (this has 0.66 B2O3, that is three times as high as a typical cone 6 glaze). The recipe on the right is the product of a project to develop a low-thermal-expansion fluid-melt transparent for cone 6 (with added colorants fluid melts produce brilliant and even metallic results and they variegate well). While the balance of fluxes (the red numbers in the formula) is pretty different, look how similar the B2O3, Al2O3 and SiO2 levels are (yellow, red and blue backgrounded numbers in the formula), these mainly determine the melting range. That means that a fluid-melt cone 6 glaze is actually just a low temperature glaze being overfired to cone 6.

Links

Glossary Zero3
The designation for a group recipes for body, glaze and engobe (by Tony Hansen), that potters can use to make low fire stoneware and porcelain

XML to Paste Into Insight

<?xml version="1.0"?>
<recipes version="1.0" encoding="UTF-8">
<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">
<recipelines>
<recipeline material="Fusion Frit F-524" amount="85.000"/>
<recipeline material="Fusion Frit F-69" amount="4.000"/>
<recipeline material="EPK" amount="9.000"/>
<recipeline material="Silica" amount="4.500"/>
<url url="https://digitalfire.com/recipe/141" descrip="https://digitalfire.com/recipe/141"/>
</recipelines>
<urls/>
</recipe>
</recipes>

By Tony Hansen


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