Many midrange and high fire glazes used by ceramic artists are what I call FLOAT glazes. These are the pretty glazes that tend to seperate out different colors in areas where the glazes are thicker. ANCIENT JASPER is this type of glaze and what it floating out is iron oxide. Iron is one of the more interesting colorants simply because it can be in so many different oxidation states. This simply means that it can make a ton of different colors. With any float glaze, enough thickness of glaze must be applied in order for the excess iron to float to the surface. If the glaze is thinly applied, the glaze will tend to be drier and a very unpleasant color.
This glaze was not developed where any massive amount of glaze needs to be applied. If it had needed this I would have told everyone on the label. We actually never had any issues getting red at all. I always try new glazes on all of our clay bodies to make sure there isn't some issue I need to know of. We also fire them at cone 5 and cone 6 to check stability. We found no issues with this glaze on either account. By now you probably saying, great but it didn't work for me. I will list some good parameters below for you to follow and I am 100% sure you will find this glaze simple to use and that it will yield great results.
1. Temperature: The red color is actually the first color to float and the use of more heat will tend to make it turn to the purples, yellows, browns and black. This means you will tend to see slightly (and I do mean slightly) more red at cone 5 than cone 6. No soak is needed for this glaze and actually soaking it will cause more red to fade into the other colors.
2. Thickness: The glaze must be applied with enough thickness to float the iron.
3. Kiln cycle: I fire all the glazes we develop in an electric kiln at fast, medium and slow speeds. Red color will be developed at all speeds but the faster the firing ~6 hours (tons of red) the better the results. I always quality check each batch at cone 5 in 8 hours. 10-12 hour cycles will cause more red to fade to the other colors. This is most critical within 200 defrees of peak. If your elements are weak and it takes the kiln a long time to achieve the last 200 degrees, you will find less red.
4. Cool down: No special cool down is needed nor will it help develop any red color. Letting the kiln simply shut off and cool naturally is all that is needed.
4. Clay Body: I have tested this on porcelain, typical stoneware bodies, bodies with grog, bodies without grog, brown colored bodies, etc. I develop red on all of them. I have found that when using our #1 Porcelain slip that the color transition away from the red tones is very pronounced (although it makes a rainbow of the other colors). This is because for a cone 5 porcelain slip alot of soft flux is needed to tighten the body. The flux in the body mixes with the glaze and actually makes the glaze softer (simulating more heat).
5. Texture: This glaze loves texture and will make some incredible colors. The texture makes the glaze get thinner and thicker in areas. The thicker the glaze the easier it is for it to stay red. The thinner the glaze gets the hotter that area of glaze gets and it shifts to the other colors.
These simple tips should help everybody that wants to make ANCIENT JASPER work. I suggest running a few tests of glaze thickness in your next kiln load and follow the firing rules above. Three nice coats on any typical stoneware body, fired to cone 5 or 6 in 6-8 hours with no soak and no special cooling curve will yield pieces just like the ones we showed in the ads. These were just pots we made in the lab. Honestly I have never actually made a pot that didn't make colors just like those pieces.
I will attempt to post a few more photos here today and next week we will post a board I made with all of our clay bodies fired at slow, medium and fast so you can see the slight differences.
Let me know if this helps.
The photo files are too big to upload. I will have someone help me make them smaller for next week.