G2934 (lower-LOI)
Recipe
Notes
This recipe was made as an alternative to blending G2934 matte and G2926B glossy to tune the degree of matteness (this being equal to about an 85:15 mix of those). Those two recipes do not require Frit 3249, they use the much more common 3134, 3124 and 3195. If you are getting started that approach would likely be better for you. This is an "MgO matte". High MgO content is a common matting mechanism at cone 10 but also works at cone 6. This recipe has the same chemistry as G2934, however, it sources the MgO from a Ferro frit 3249 and talc rather than from dolomite. This specific frit is the secret to why this glaze works. If you do not have it and do not know how to do the chemistry to substitute another MgO-sourcing frit, then you must use the G2934 recipe. The use of a frit to source MgO in this recipe produces a much lower LOI (3.8 vs. 13.6), a smoother fired surface and better melt fluidity to host stains (stains look fantastic in this base). Glazes that have MgO levels, including this one, can have crawling issues with certain stains or opacifier additions, especially inside extreme concave contours (e.g. handle joins). Make sure wet glaze slurry wets all inside angles and is not applied too thick. And make sure the glaze dries quickly (glaze inside and outsides separately if needed to avoid water logging the bisque). WARNING: Like the original, the degree-of-matteness is very dependent on cooling rate. Fast cooling (e.g. free-fall in a lightly loaded or smaller kiln) produces a silky matte surface. Slower cooling (e.g. a heavily loaded kiln) produces a matter and drier surface (subject to cutlery marking). Test in your circumstances to decide whether to adjust your firing to accommodate this or blend in some glossy G2926B produce the silky surface. Fusion Frit F-69 can be used instead of Ferro Frit 3249 (actually, it is better). This recipe employs a mix of calcined and raw kaolin to keep the drying shrinkage down (to avoid cracking on drying). If you use pure kaolin it will likely crack during drying. If you do not have calcined kaolin just make your own (bisque fire a container of powder). This glaze has a very low thermal expansion and will not craze on any common clay body. It accepts stains exceptionally well. It is low enough that on some clays it will be under too much glaze compression, this could lead to dunting. Use G2934Y2 if this is an issue. We recommend doing cutlery marking tests on your ware. If they mark, blend in a little transparent glossy glaze (like G2926B). This will compromise the matteness a little but will reduce the marking. Again, although matte in appearance, this glaze has a high melt fluidity. That means that brush-on colors could bleed. Because this contains both calcined and raw kaolins you can adjust their ratios to control the compromise between dry hardness and drying shrinkage. If better gelling response to Epsom salts (or other flocculant) is needed trade one or two percent raw kaolin for bentonite (to increase the particle surface area). 1100 water, 1000 powder to get a creamy mix. Regular 2934 (with dolomite) took more water, about 1300. Nicer surface than G2934, same matteness, better fluidity. Mixing notes: Joe: April 29/19 Mixed up a batch and added 10% Mason #6021 Red stain. Final totals were: G2934Y + 10% stain weighed 5045 grams. Water weighed 5450 grams. Let the glaze sit for 3 days to saturate before adding final water to bring to an S.G. of 1.43 and viscosity was approx. 12 seconds with Ford Cup. At these quantities, the final ratios would be: Glaze powder (including stain) 48% Water 52% This mixture yielded about 7.3 litres of mixed glaze. This glaze was screened 80 mesh and has no Epsom salts added.
Description
The same chemistry as the widely used G2934 but the MgO is sourced from a frit and talc instead of dolomite. It has a finer surface, less cutlery marking and staining.