G1916M, G1916Q expansion adjustable low fire clear glazes

COE Adjustable Low Fire Clear Glaze

Total:100.00

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Notes

*Update Jan 2023:
This glaze has a higher thermal expansion than recipes we have developed since. It is published here for learning purposes.

The main challenge in making a low-fire clear glaze work is making it 'fit' (having a thermal expansion as similar as possible to the clay). While the lack of a good glaze interface makes this a more difficult task, it also makes it easier to test. Hot water:ice water stressing of the ware is much more likely to show crazing or shivering and thus you can adjust the recipe to compensate.

Most frit manufacturers have a selection of low-fire boron frits which exhibit a variety of thermal expansions. Many of these are complete glazes with the simple addition of a little kaolin. The thermal expansions of these frits are published. Thus you can mix a glaze, stress-test it (using the GLFT test), then blend in another frit whose expansion will adjust the glaze's overall expansion in the correct direction to eliminate any fit problems.

Ferro has three frits of the type mentioned above: 3134, 3124, 3195.
Since frit 3134 has the highest expansion, increasing it will decrease shivering. Increasing low expansion frit 3124 will decrease crazing.

Another frequent problem with low-fire boron glazes is 'clouding'. A transparent glaze will appear cloudy and have a bluish haze if there is micro-bubble development or crystallization of calcium-borate. We have used 20% kaolin (rather than 10) in the glaze included here for this reason (kaolin sources alumina). If you decrease the amount of kaolin the glaze will melt better but crystal development may increase. If you soak the firing and bisque the ware higher than the glaze firing the glaze bubbling should be minimal. The glaze includes 5% flint as an extra measure against crazing. If this glaze does not melt well enough at cone 06 you might consider firing to 04 or 03.

This glaze base is suitable for all types of glazes. For colors, add 1-10% stain; for opacity use 5-15% zircopax, superpax or tin; for variegation of the surface use 1-7% rutile or titanium; for speckle add .1-.5% manganese granular (or similar material).

For an overview of the Majolica process, see the Magic of Fire, Vol 2 and the web page http://digitalfire.com/magic/majolica.htm

This glaze can also be made into a matte by the addition of light magnesium carbonate. The amount required needs to be carefully tested. In our circumstances, 11-12% works well to produce a hard scratch-resistant surface. If you use more the glaze will have small bubbles in the surface.

Pictures

G1916M 3124:3134:Kaolin:Silica Adjustable Clear on mug

Buffstone with G1916M at cone 03 (1950F) - crazing

L212 (right) with G2931L is shivering.
These glazes should be switched.
Firing was held at 1850 for 30 minutes on the way down and 200F cooled to 1400F.

G1916M applied very thick on new mix L215

No crazing after months. Fired 04. Milky because of thickness.

Cone 05+ Expansion Adjustable Gloss Base

Total:100.00

Auto Unity Formula + Analysis

Notes

*Although similar to the previous G1916M, this recipe provides greater thermal expansion adjustability. It combines a middle-of-the-road thermal expansion frit with a very low and very high expansion frit (they cancel each other out but increase gloss of the otherwise silky Frit 3195). The frits in this recipe are common (the 3249 less so but it deserves to be common because of its utility). We adjusted this in a later version, G1916QL1, it employs a kaolin for better clarity and more frit 3249 for glaze fit on more bodies.

This melts well from cone 05 and is stable to cone 2 or higher.

Do not assume the glaze fits because a piece emerges from the kiln without crazing or shivering. Thermally stress it (by two minute boiling-water and ice-water immersion cycles). We refer to this as the 65:10:10:15 recipe.
If this crazes, try 65:20:15 (3195:3249:EPK).
If it shivers, use 65:20:15 (3195:3110:EPK).
If the problem persists reduce the 3195 and increase the other (e.g. 55:30:15).

The ball clay also imparts good working properties and it has a lower LOI than EPK (to generate less micro-bubbles in the glaze).

Add 2% iron oxide to this when using on terra cotta bodies to enhance their red, the iron particles also act as a fining agent to remove the microbubbles they produce.

Because this employs ball clay, it the glass will have a slightly amber color (from the Fe2O3 in the clay). If that is an issue, try using a kaolin instead (we recommend New Zealand or Grolleg, the G1916Q2 and G1916Q3 variations do this).

Although drop-and-soak firing schedule helps clarity of transparent glazes at higher temperatures this glaze will produce crystal clear results with fast firing. However, it is high boron, normally such glazes have more issues with bubble clouding. But we have found that this one, if not applied too thick, fires crystal clear (likely its high Al2O3/SiO2 is the reason).

We find that 3800 water for 4000 powder produces ~1.44SG. The slurry gels more than with EPK, Grolleg or NZK.

Pictures

G1916Q at Cone 01 on 3D+iron

Very nice results on L3724E red body at cone 01. Piece is very strong.

1916J and Q fired to 1450F

These glazes are starting to melt, the surface having reached the consistency of a porcelain and have densitfied to very low porosity. Notice the iron in the ball clay really shows up at this stage (it will be less evident later).

G1916Q Cone 04 using 04DSSC schedule

Counterclockwise: L212, Raku, Buffstone, L213, L210, L215
Crazing out-of-the-kiln on Raku and buffstone.
Bisque 04-03.

G1916Q and J fired 1650-2000F

Ten-gram balls melted and flattened as they fired. They soften over a wide range, starting well below cone 010! At 1650F carbon material is still visible (even though the glaze has lost 2% of its weight to this point), it is likely the source of the micro-bubbles that completely opacify the matrix even at 1950F (cone 04). This is an 85% fritted glaze, yet it still has carbon; think of what a raw glaze might have! Of course, this is a thick layer, so the bubbles are expected. But they still can be an issue on a piece of ware. So to get the most transparent possible result it is wise to fire tests to find the point where the glaze starts to soften (1450F in this case), then soak the kiln just below that (on the way up) to fire away as much of the carbon as possible.

Success with cyrstal clear glaze cone 03

Uses Cone 03 soak-soak-slow cool schedule.
Left: P6282 with 3685U slip and 1916Q. Clear and very good. Glaze is thicker than the other two. Shivering on lip, the slip is not fitting the body.
Center: P6282 with G2931F Ulexite clear. Better clarity even though it is applied very thin. Shivering on lip, the slip is not fitting the body.
Right: L3724F with 3685U slip. No shivering. Very good coverage of the glaze, very clear, the best I have seen yet!

G1916Q on L215, L212, L210, L213, Buffstone at cone 03

All exited from the klin without crazing. The L215, L213, L210 and L212 samples subsequently survived a 300F/Icewater test without crazing, but the Buffstone did not. The L213 would not likely survive a cold-to-hot test without shivering.

1916Q cone 04, 03

Both were slow cooled. While the cone 04 version is glassy and ultra-gloss, it has significant clouding of micro-bubbles. The cone 03 version, right, is completely transparent.

G1916Q on L210 fired at cone 04

Has survived for a year without crazing.

G1916Q+2%Iron on L212 talc body fired at cone 05

This will likely shiver over time. But the speckle that happens on white bodies is clearly visible.

G1916Q applied thickly on L215 fired cone 04

No crazing after 2 months.

G1916Q on L4170 cone 04

Thin application is clearly the way to get the best transparent. The glaze eventually craze where application is thicker.

G1916Q with Iron Fining Agent

Total:102.00 (R)

Notes

*This recipe will fit L215 and give it a deep rich-looking red color when fired to cone 04 with a drop/soak/slow cool firing schedule. If too thick it will probably show signs of cloudiness, but it is pretty decent if applied correctly.
The secret is the Iron Oxide Red acts as a "fining" agent to minimize the boron bubbles in the glaze.
THIS GLAZE MUST BE SCREENED AT LEAST 80 MESH. (100 mesh is even better). The reason for this is to dissipate Iron Oxide Red properly into the glaze so it can better act as the fining agent.

Glaze Firing Schedule as follows:
R1. 150 - 250 Hold 60
R2. 350 - 1795 Hold 0
R3. 108 - 1900 Hold 15
R4. 999 - 1800 Hold 30
R5. 150 - 1400 Hold 0 / Off

This will be in the cone 04 range with cone 04 bending.
Ramp 5 is optional, more for important ware, than perhaps decorative pieces.

Mix glaze at a 50/50 ratio powder/water by weight and allow to sit overnight for Iron Oxide Red to saturate prior to screening. Adjustments may have to be made, but this will put you in the range of an acceptable dipping glaze on the low end S.G. of 1.40 or slightly higher.

Pictures

2% iron in G1916Q acts as a microbubble fining agent

Both pieces are the same clay body, Plansman L215. Both are fired to cone 03. Both are glazed using G1916Q borosilicate recipe. The glaze on the piece on the left has 2% added iron oxide (sieved to 80 mesh). Each particle or agglomerate of iron (which is refractory in this situation) acts to congregate the micro-bubbles so they can better exit the glaze layer. Notice also how much richer the color is as a result. The piece on the right, without the added iron oxide, is neither as red nor as transparent. Of course, I had to be careful not to apply the glaze too thickly on both.