|Monthly Tech-Tip |
Alternate Names: New York Slip, Albany Clay
Albany was a low plastic silty clay that was mined in Albany, New York for many decades. It melts to a glossy chocolate brown glaze at cone 8-10. It was a very popular glaze ingredient for dark colors and tenmoku and iron crystal effects. In the early 20th century it was used extensively on heavy utilitarian stoneware across North America and even on electrical insulators. Glazes could be formulated very easily using this material as a starting point since it was already balanced and had good slurry properties. Potters especially adopted this material and it appears in thousands of recipes used across North America.
There are a number of substitutes for Albany and anyone with ceramic chemistry calculation software can easily speculate on a mix of materials that matches the chemistry on paper. However keep in mind that judging the similarity to Albany is a complex issue of mineralogy, physical properties and chemistry and it depends on the reliability of the information at hand on what Albany actually was.
This shows the soluble salts in the material and the characteristic cracking pattern of a DFAC test disk when made from a low plasticity clay. Notice the edges have peeled badly during cutting, this is characteristic of very low plasticity clays.
These are three runs of Alberta Slip being compared with the original Albany Slip. These are ten-gram GBMF test balls fired on porcelain tiles at cone 6. This test shows how the material flows, how much gases of decomposition it generates and how well it allows them to escape. As you can see, they are very similar in melting behavior.
These three melt flows and mugs were fired at cone 6 (using the C6DHSC firing schedule). The benchmark recipe is 80% clay and 20% Ferro Frit 3195. The center melt flow and mug (made from a Plainsman 3D-based stoneware) employs original Albany Slip as the clay portion. The one on the far left uses an Albany Slip substitute that was developed by calculating a mix of RedArt and other materials to have the same chemistry as Albany Slip. The one on the right employs Alberta Slip. Notice that, although the Alberta Slip version has a very similar melt flow, on the mug it is apparent that it needs a little iron oxide for a better match (e.g. 1-2%). And the glaze on the left: The chemistry of RedArt is different enough from Albany that some compromises in chemistry-matching were needed to avoid over-supplying the iron even more (and firing even darker than this). Although this Redart version runs in a very similar pattern on the melt flow, the character of the glaze is somewhat different on the mug (a better match can be achieved by increasing the frit percentage slightly, or firing to cone 7).
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.
Albany Slip was a pure mined material, Alberta Slip is a recipe of mined materials and refined minerals designed to have the same chemistry, firing behavior and raw physical appearance.
Lithium, albany glaze at cone 5 using original albany slip
Outside glaze is G2934Y black. Inside is 80% Albany clay and 20% Ferro Frit 3195, a really stunning glaze! I used the C6DHSC firing schedule. The body is a natural porcelain that vitrifies beyond the zero porosity point, producing incredibly strong ware. Yet it does not warp during firing.
Sheffield Slip substitute
GA10x-A - Alberta Slip Base for cone 10 oxidation
Alberta Slip creates a glossy transparent brown at cone 10 with the simple addition of 10% frit.
GA10-A - Alberta Slip Base Cone 10R
Alberta Slip at 60:40 calcine:raw makes a great tenmoku-like glaze at cone 10R
Clays that are not kaolins, ball clays or bentonites. For example, stoneware clays are mixtures of all of the above plus quartz, feldspar, mica and other minerals. There are also many clays that have high plasticity like bentonite but are much different mineralogically.
|Sieve Analysis Wet||on 60 mesh: 0 on 120 mesh: 1.0% on 200 mesh: 5%|
|Frit Softening Point||1170C|