G2934 Cone 6 Matte Base Glaze G2926B Cone 6 Clear Glossy Base Glaze GA6-B Alberta Slip Cone 6 Base GR6-A Ravenscrag Cone 6 Base L3954B Mid Temperature Engobe G1916Q Transparent Base Glaze G1947U Transparent Base - Cone 10R G2571A MgO Matte Base - Cone 10R GR10-A Ravenscrag Slip as-a-glaze - Cone 10R L3954N/J Cone 10 Engobe Base
G2934 Cone 6 Matte Base Glaze
For Stonewares and Porcelains.
A dolomite silky matte for cone 6. It fires translucent rather than completely transparent (because it is a matte). If you want pure white, add Zircopax (start with 5%, but keep it at a minimum to minimize cutlery marking). There is more information on this at the Digitalfire.com page on G2934.
G2934 Cone 6 Matte base (upper left sample) with various stain additions. A porcelain body, M370, has been used (bright colors do not work on dark burning bodies unless you underlay them with an engobe). Mason 6020 is a body stain, it does not work in glazes (as you can see here). Mason 6006 also does not work (because this glaze does not have enough CaO in the chemistry).
The degree-of-matteness is very dependent on cooling rate. Fast cooling (e.g. free-fall in a lightly-loaded or smaller kiln) produces our desired silky matte surface. Slow cooling (e.g. a heavily loaded kiln) produces a more matte and drier surface (subject to cutlery marking). Do test firings to determine if you can adapt your firing to this recipe or need to adapt this recipe to your firing. If the latter, blend in some glossy G2926B to shine it up to the degree needed.
It is standard practice to fire cone 6 using a hold (or soak) at top temperature schedule (e.g. for 30 minutes) to produce a defect-free glaze. However we recommend the drop-and-hold PLC6DS firing schedule. Both require manual programming of your kiln (because none of the built-in programs do any kind of hold). If you have not manually programmed your kiln, this is a barrier you need to cross to produce more defect-free glaze surfaces.
G2934 matte is an excellent color base and works particularly well with inclusion stains. However, each different color created will likely require fine-tuning the degree of matteness. It is already quite matte, shine it up slightly by blending in some clear glossy G2926B (click here to see an example).
There is nothing intrinsically toxic in the recipe, so by itself it is not a leaching hazard. But additions of metallic colorants will change that, consider doing a GLLE test to verify (it is generally best not to employ glazes having high percentages of colorants on food surfaces).
The body is Plainsman M390. These are commonly used base glazes. The top one is an MgO matte, the next is a calcium matte. They behave very differently to these additions. Notice also that thickly applied titanium dioxide is very different. Tin oxide fires whiter than zircon (e.g. Zircopax).
G2934 is not suitable on M390 (either with or without zircopax). This is an example of the best we can achieve, it was fired using the C5DHSC cone 5 firing schedule (cone 6 pinholes more). Dark bodies generate more pinholes, despite the slow cool they have not all healed. Inside glaze is GA6-B.
When mixed with water to create a thixotropic slurry, this will perform well as a dipping glaze. It will apply evenly to bisque, produce minimal dripping and dry within seconds. It will be adequately durable for handling. If bisque walls are thin, it will be necessary to glaze the inside and outside of pieces as separate operations (with a drying time between).
Glaze Fit: This glaze recipe has a low thermal expansion. That means it will fit, without danger of crazing, on any body we make. However, under some circumstances, it could shiver. If this happens, consider using the G2934Y2 variation, it has a higher thermal expansion (as noted above, if it is too matte blend in some glossy G2926B).
If you are glaze layering (using this as a dipping glaze and painting a commercial gummed brushing glaze over it) there is a risk of crawling. It may be necessary to add some gum to this, converting it from a dipping glaze to a base-coat dipping glaze.
Adding the Stains and Opacifiers: Simply multiply the weight of the amount of powder you want to use and divide by 100. For example, if you have 2000 grams of glaze powder and want to add 6% stain: 2000*6/100=120 grams of stain. Or, 10% zircopax: 2000*10/100=200 grams of zircopax (stain %'s are suggestions, for some colors you may need more, testing is needed). Bright colors and whites will be muted on dark-burning bodies.
If you just want to mix it the traditional way, start with about 85 water to 100 powder (by weight) and mix well using a propeller mixer. Add more water until it is creamy, try it, adjust, etc. To learn more visit the G2934 page at the Digitalfire Reference Library.
If you want better application properties (as a one-coat dipping glaze) we recommend targeting a specific gravity of 1.43-1.44 and gelling the slurry to make it thixotropic (see next paragraph). Water weight: Powder weight x 0.9. Yield is about 1.4 litres per kg of dry powder.
To prepare for use as a single layer dipping glaze, add the powder to 90% of the water and mix until it flows well. Then add water to get the right specific gravity. Sieve through 80 mesh.
For the best working properties we want the slurry to be thixotropic (our thixotropic glazes gel after motion stops, they "bounce-back" on final stop-motion after stirring, in 2-5 seconds). A flocculant is added to achieve this (e.g. start at 1g of epsom salts per 1000g glaze powder). Be careful when adding the flocculant, it is easy to add too much and get a bucket of jelly (if that happens re-thin it by adding, Darvan by-the-drop). When the slurry is right, you can two-second-dip a piece and on withdrawal it will drain well, only a few drips will fall and on turn-over it will not run back down. It will apply evenly on dense or porous bisque. This "rheological state" can change on storage so be ready to adjust it later. Also recheck the specific gravity from time to time and, if needed, adjust by adding or removing water.
The body is Plainsman M340S. Cone 6. Left to right: G1214Z calcium matte base glaze with 6% titanium dioxide added. GR6-A Ravenscrag base with 10% zircopax (zircon). G2926B glossy transparent base with 10% zircon. G2934Y silky magnesia matte base with 10% zircon.
G2934 with yellow stain (left) vs. a glossy glaze (G2931K with the same yellow stain but fired at cone 03). The matte surface is much easier on the eyes for bright colors (and much more pleasant to the touch).
Right pail: 2 gallons of G2934 base with 10% Cerdec yellow stain. Cost: $135. Jars with the same amount: Almost $300! And you have to paint them on in three coats with drying in between. The one in the pail is a true dipping glaze. You can dip a bisque mug for 2 seconds and it dries immediately in a perfectly even layer (if mixed according to our instructions).
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|Plainsman Clays Ltd.|
702 Wood Street, Medicine Hat, Alberta T1A 1E9
Phone: 403-527-8535 FAX:403-527-7508