|Monthly Tech-Tip |
Modified: 2023-09-16 16:18:58
An amber-colored glaze that produces a clean, micro-bubble-free transparent glass at cone 5-6. Works well on brown and red burning stonewares.
|Alberta Slip 1000F Roasted||40.00|
|Ferro Frit 3195||20.00|
|Red Iron Oxide||2.00|
Alta known as GA6-B at PlainsmanClays.com.
The successor recipe to GA6-A (this uses Ferro Frit 3195 or the equivalent Fusion F-2 instead of 3134). It fires to a more brilliant glossy and durable surface and has become the standard go-to honey/amber base recipe for Alberta Slip at cone 5 or cone 6. We recommend the C6DHSC or C5DHSC firing schedules.
We recommend the addition of 2% iron oxide to get a richer color. The iron has an added benefit: It gels the glaze (the 2% is low enough that it does not over-gel, it just produces a nicer-to-use slurry, one that goes on more evenly).
This recipe fires to a lower thermal expansion than GA6-A did (by virtue of higher B2O3, Al2O3 and SiO2 levels) so will solve any crazing issues you may have had. For an even lower expansion and better melting version consider using L3500G, it is made using Ferro Frit 3249.
The chemistry in this is not compatible with the rutile blue version (see picture below). In addition, this one also does not crystallize on slow cooling the way GA6-A does.
If you need even better durability, this will likely accept 45 micron silica additions without loss of gloss, especially at cone 6. Start by adding 5% (then 10%). The more it will take the harder it will be.
One caveat: This base will not produce floating blue effects with rutile or titanium additions, the GA6-A base is needed for that.
Roasted Alberta Slip (right) and raw powder (left). These are thin-walled 5 inch cast bowls, each holds about 1 kg. I hold the kiln at 1000F for 30 minutes. Why do this? Because Alberta Slip is a clay, it shrinks on drying (if used raw the GA6-B and similar recipes will crack as they dry and then crawl during firing). Roasting eliminates that. Calcining to 1850F sinters some particles together (creating a gritty material) while roasting to 1000F produces a smooth, fluffy powder. Technically, Alberta Slip losses 3% of its weight on roasting so I should use 3% less than a recipe calls for. But I often just swap them gram-for-gram.
The difference is a slow-cool firing. Both mugs are Plainsman M340 and have the L3954B black engobe inside and partway down on the outside. Both were dip-glazed with the GA6-B amber transparent and fired to cone 6. The one on the right was fired using the PLC6DS drop-and-hold schedule. That eliminated any blisters, but some pinholes remained. The one on the left was fired using the C6DHSC slow-cool schedule. That differs in one way: It cools at 150F/hr from 2100F to 1400F (as opposed to a free-fall). It is amazing how much this improves the brilliance and surface quality (not fully indicated by this photo, the mug on the left is much better).
The body is dark brown burning Plainsman M390 (cone 6). The amber colored glaze is 80% Alberta Slip (raw:calcine mix) with 20% of each frit. The white engobe, L3954B, on the inside of two of the mugs is L3954A (those mugs are glazed inside using transparent G2926B). The Alberta Slip amber gloss glaze produces an ultra-gloss surface of high quality on mugs 2 and 3 (Frit 3249 and 3195). On the outside we see it this glaze on the white slip until midway down, then on the bare red clay. The amber glaze on the first mug (with Frit 3124) has a pebbly surface. These are fired using a drop-and-soak firing schedule. Some caution is required with the 3249 version, it has low thermal expansion (that is good on bodies that normally craze glazes, but risks shivering on ones that do not).
GA6-B (left) is our regular Alberta Slip honey glaze (20:80 Frit:Slip). But the G3903 (mislabelled L3903 here) uses Fusion Frit FZ16, the champion melter of all the frits we have tested. It produces a surface so brilliant it is hard to believe the frit is not leaded. And notice how it has eliminated the bubbling. The G3903 works well down to cone 4.
Making black using metal oxides normally involves cobalt oxide, manganese dioxide, copper oxide and iron oxide. Combined they typically comprise 10-15% of the recipe. Using the Alberta Slip GA6-B base recipe, only 4% Mason 6600 black stain is needed to get a jet black! These blacks were applied in varying thickness on a porcelain and buff stoneware before having the white second layer applied. The black glaze on the top-right tile only has 3% stain. The overglaze is a gloss white with increasing amounts of tin oxide added (4-7%). Beyond 5% there appears to be no advantage.
Fired at cone 6 using the C6DHSC schedule. On Plainsman M340 and Buffstone. Left: Alberta slip with 20% Ferro frit 3195 (GA6-B). Right: Alberta Slip with 20% Fusion Frit FZ-16 (G3903). This Fusion zinc frit is a super-melter, much better than 3195. A picture cannot do this glaze surface justice! The zinc brings out the red coloration much better. Frit FZ-16 is not readily available, we are hoping companies will eventually stock it. And it produces a more brilliant glassy surface that highlights thickness variations even better. Adding a little extra iron oxide (e.g. 1-2%) would make the effect even richer. One thing to keep in mind: These frits upset the development of rutile or floating blue effects.
Fired to cone 6 using the C6DHSC schedule. Top: GA6-B. This recipe is 80% Alberta slip and 20% Ferro Frit 3195 (we used to use frit 3134 but have found frit 3195 works much better). Bottom: We added 1, 2, 3 and 4% iron oxide. At about 2%, the color matches the rich reddish effect you would get if you used an 80:20 Albany:3195 recipe (without an iron addition). An added benefit is that the iron acts as a fining agent to remove micro-bubbles to achieve better transparency.
Hand built. Cone 6 drop-and-hold PLC6DS firing. The engobe is the L3954B base recipe with added Mason 6600 black stain, it was applied at the leather hard stage inside and part way down the outside. The GA6-B glaze enhances the black under it. By Tony Hansen.
GA6-A - Alberta Slip Cone 6 transparent honey glaze
An amber-colored glaze that produces a clean, micro bubble free transparent glass on brown and red burning stonewares.
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|By Tony Hansen|
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