The Mason reference guides states that this "can be used as a 'body stain' in porcelain at high temperatures". However we find that it works well as a body and engobe stain at any temperature. They indicate a maximum firing limit 2300 degrees F (1260 degrees C) and that free zinc oxide influences the color more than any other element. They state that "generally, zincless glazes should not contain magnesium oxide". However the G2934 is a zinc-free high-MgO matte and this stain works very well, even at low percentages.
Old Number: 158
A gunmetal glaze I have wanted for decades!
After 40+ years of making pottery I finally have a perfect functional, durable gunmetal black. It has an incredible silky surface. It does not cutlery mark. It does not craze on anything. It is easy to clean. This is G2934Y with 6% Mason 6600 black stain firing using the PLC6DS schedule. I had to tune it a bit, adding about 15% glossy G2926B, because it was a little too matte on initial firings. But now it is perfect. These are heavy mugs made using the M340 casting recipe (and the casting-jiggering process). The speckled mug was made by casting a thin layer of the speckled version of the slip first, then filling the mold with the regular slip. I used a 40-minute cast to get walls nice and thick!
L3954J black engobe on a cone 10 whiteware body
The body is Plainsman H570 (0.5-1% porosity). Notice the EBCT (engobe compatibility) test bars in front. These sandwich the body and the engobe together in a thin strip, differences in fired shrinkage curl the bar during firing (toward the higher shrinker). The straighter the bars fire the better the fit. My regular engobe for use on our buff stoneware, L3954N (Plainsman H550, 2-3% porosity), has lower fired shrinkage than this (since that body is less vitreous). This one increases the shrinkage (with 5% more nepheline syenite, 5% less silica and 3% less ball clay). This employs 10% Mason 6600 stain to produce the jet-black fired product.
Stunning black silky matte glaze at cone 6
This contains 6% Mason 6600 black stain (Mason 6666 gives dark brown, don't use it). The base recipe, G2934, is an excellent balanced-chemistry host for a wide range of stains to produce equally stunning reds, yellows, oranges, etc. The fritted version of the recipe, G2934Y, provides an even better host. This glaze is affected by the clay it is on. The body on the right is highly vitreous, this has produced a finer texture that glistens in the light. The body on the left is a whiteware having 1% porosity (Plainsman M370). Firing schedule is also a factor, slower cooling will dull the color more. We use the PLC6DS firing schedule.
Absolutely jet-black cone 6 engobe on M340
This is the L3954B engobe recipe but it has 15% Mason 6600 black body stain (instead of the normal 10% Zircopax for white). There is no cover glaze, yet it is durable and absolutely coal black (so a lesser stain % is possible). We have updated the mixing instructions at PlainsmanClays.com and Digitalfire.com pages (showing exact amounts for water, powder, Darvan) and the text on the glossary pages about thixotropy and engobes (read these again and learn to use the engobe process even better). This engobe base is designed to work on regular M340/M390 stonewares (not porcelains). This is exciting because these bodies are so much more robust in drying and much less expensive than porcelains.
Tuning the degree of gloss on a matte black glaze
These 10 gram balls were fired and melted down onto a tile. The one the left is the original G2934 Plainsman Cone 6 MgO matte with 6% Mason 6600 black stain. On the right the adjustment has a 20% glossy glaze addition to make it a little less matte. Notice the increased flow (the ball has flattened more) with the addition of the glossy. In addition, while the percentage of stain in the one on the right is actually less (because it was diluted), the color appears darker! Tuning the degree of matteness when making color additions to a base is almost always necessary to achieve a glaze that does not cutlery mark.
Mason stains in the G2934 matte base glaze at cone 6
Stains can work surprisingly well in matte base glazes (provided they are not too matte). Stains perform differently in a matte host glaze. The glass is less transparent and so varying thickness do not produce as much variation is tint. Notice how low many of the stain percentages are: yet most of the colors are still bright. A good reason to minimize stain concentration is to avoid leaching. We tested 6600, 6350, 6300, 6021 and 6404 overnight in lemon juice, they passed without any visible changes. It is known that MgO mattes, like this one, are less prone to acid attack that CaO mattes. A down-side to this matte mechanism is that chrome-tin stains do not work (e.g. 6006), this is because this does not have the high CaO content needed in the host glaze to develop the color. The inclusion stains 6021 and 6027 work very well in this base. As do the 6450 yellow and 6364 blue. And the 6600 produces an incredible gunmetal black. The 6385 is an error, it should be purple (that being said, do not use it, it is ugly in this base).
Mason stains in the G2926B base glaze at cone 6
Stains are a much better choice for coloring glazes than raw metal oxides. Other than the great colors they produce here, there are a number of things worth noticing. The percentages may be lower than what you think would be needed, stains are potent colorants. Staining a transparent glaze produces a transparent color, that means it is more intense where the glaze layer is thicker. This is often desirable in highlighting contours and designs. If you add an opacifier, like zircopax, the color will be less intense, producing a pastel shade the more you add. The chrome-tin maroon 6006 does not develop well in this base (alternatives are G2916F or G1214M ). The 6020 manganese alumina pink is also not developing here (it is a body stain). Caution is required with inclusion stains (like #6021), the bubbling here is not likely because it is over fired (it is rated to cone 8), adding 1-2% zircopax normally fixes this issue.
Polar Ice Porcelain with Body Stains - by Robert Barritz
Robert has done really valuable work in this research, what an amazing range of color! I am so grateful he shared this with the rest of us. Surfaces are unpolished and unglazed. All are fired to cone 6. Browns are missing, they can be made using iron oxide. For blacks, Mason 6600 is also effective. The blues require lower percentages than shown here, as low as 2% can be effective. Likewise with others, there is an optimal amount for each stain, beyond that, with increases in percentage the color intensity increase will drop significantly. There is another reason to keep stain percentages to a minimum: To reduce the impact on body maturity (and firing shrinkage). Blues, for example, can significantly heighten the degree of vitrification, even melting the porcelain. If you plan to marble different colors, keeping stain percentage as low as possible is even more important, unless you can do fired shrinkage compatibility testing, for example, the EBCT test. Need to develop your own white porcelain? See the link below.