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| L & L Doll Test Kiln |
The circular shelves that L & L sells were a bit thick for so small a kiln so I purchased thinner high alumina shelving from Bailey Ceramics Supply and then cut the rectangular shelves to a hexagonal cardboard template that would maximize the load space for this tiny kiln. The shelves are sized to allow approximately 1/2 inch circulation space between the shelf and the kiln walls. One shelf has the front edge cut back so the cone can be placed in front of the spy hole without striking the front shelf edge.
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| Shelves and Posts |
Cutting high alumina shelves is not too difficult, assuming one has the appropriate tools. The ferocious water cooled cutting beast (shown below) with diamond edged blade and 1.5 hp motor (that I salvaged and rejuvenated some years ago) allowed the cutting process to be quickly accomplished. Small left over scraps were trimmed into tiny shelf posts, using the same machine. I measured the height of my tests tiles, so the cut posts would maximize the kiln load.
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| Diamond Cutting Saw |
For the second test firing, I decided to concentrate on the Bailey's Red with 12% red iron oxide (Spanish Red was used), hoping I could achieve the same vibrancy and stability when applied to functional ware created at Maine Kiln Works. I have been using GlazeMaster to record and update my tests. It is a resourceful program for creating line blends, developing glazes, and creating batch sheets for glaze tests. Created by John Hesselberth of Frog Pond Pottery, it is a glaze calculation program (designed for studio potters) which can also be used for clay body recipes.
For this particular test firing, I created a larger batch of Baileys Red 12% red iron oxide. Using GlazeMaster, I expanded the glaze batch to 5000 grams from the 100% base recipe. Below is the glaze recipe published in John Britt's book. This is base glaze I am testing with 12% iron oxide substituted for the original 8%.
Kaolin - EPK 13
Felspar - Custer 47
Talc - 10.5
Bone Ash - 14
Silica - 13
Lithium Carbonate - 2.5
Iron Red Oxide -12
I tested the glaze line blend over stoneware and porcelain mugs and flat dishes in order to get a contrast between horizontal and vertical glaze effects with the same glaze thickness. All the pieces were applied been dipped for timed interval into the 5000 gram batch.
I kept the firing schedule the same, repeating John Post's recommended 150 F / H slow cooling ramp from 1800F to 1300F. These are some of the results from this firing.
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| Stoneware Dish |
With slight variations, the 12% iron oxide Bailey's Red test revealed the above result on this stoneware chowder bowl. It did not however, create a similar effect on the porcelain dish. The formation of iron red crystals on the surface did not form to a great extent, and left the porcelain with predominantly brown > black tonal range with very little red crystal development.
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| Porcelain Dish |
Likewise the mug results showed the same browner tone over the porcelain example as shown in the centre, with the left and right mugs showing the slow cooled iron red over my shop developed T68 stoneware.
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| Bailey's Red 12% over Stoneware (L,R) and Porcelain (C) |
The iron in the stoneware body must play some role in the formation of iron crystals on the surface of the glaze. As there is very little to no iron content in the porcelain body, then the results achieved are different. If anyone is working in a similar process and their results are different on the porcelain, please leave me feedback, it would be greatly appreciated! It would interesting to achieve a good iron red over porcelain as well.
I recognized a slight difference in color and crystal formation from the previous firing, noting that Bailey's Red did not turn out as bright as the previous firing results. I have taken into consideration glaze application and thickness are crucial in achieving a bright iron red. I will fire the kiln again, and consider modifications to glaze thickness as well as the cooling ramp. My initial thoughts after this firing is to make another line blend but vary the thickness of the glaze. I am also going to take up John Post's recommendation of adjusting the cooling temperature from 150F per hour to 125F per hour from 1800F to 1300F. My next post will display these results.
My generous thanks to John Post for his explicit and very helpful suggestion which have definitely put me on the right track with the beautiful and somewhat unusual oxidation glaze effect.
Only a bit unrelated to the current subject—I will be posting blogs with information which will detail a very effective process for cutting the very hard St Gobains Advancer (distributed by kilnshelf.com) kiln shelves that are both expensive and widely used due to their strength, longevity and flat firing qualities. One would think their hardness would make them virtually impossible to cut but they are actually fairly easy to cut if one knows what process to employ. The solution is water jet technology which is widely available in many locations. Stay tuned for more information in this regard.
