Dad used to say that he could spend the rest of his life experimenting with different ways to use Crackle White Raku Glaze and never get bored. Mom’s been repeating that a lot over the last couple of months, as I’ve been doing my super secret covert Raku firings that she always seems to find out about. So finally, I took the hint and instead of trying to hide my Raku firings from her, I decided to involve her in this one. In keeping with the Independence Day theme, I chose Dad’s Crackle white Raku glaze to provide the white in the red, white and blue theme. In fact, I mixed up three versions of just crackle white. One using Gerstley Borate, one using Laguna Borate and one using Gillespie Borate:
Shown at left (click to enlarge), the recipe mixed up with Gerstley Borate gives good tight crackles, which are more noticeable when the glaze is applied thicker or in multiple coats. On the right is the same recipe, but with the synthetic alternative, Laguna Borate used in place of the Gerstley. In this formulation, the cracks are much larger and more pronounced. Below, the Gileespie Borate example contains elements of both Gerstley and Laguna borate, yielding some large crackles and a a lot of little small rounded crackles. The Gillespie Borate also has a much dirtier appearance and a somewhat silvery metallic effect.
From hosting two Steve Branfman workshops, I learned that various commercial glazes and underglazes can be applied to a piece and then covered with the crackle white (which is actually clear, not white at all). I tested two pieces this way. Shown at right is a porcelain bowl which was textured with a thick slip. AMACO Velvet Underglazes were then applied to the bone dry greenware, slighltly overlapping them. The clear glaze mixed up with Gerstley was then applied. At left is a handbuilt cylinder, using Raku clay, textured and underglazed at the leatherhard stage, bisqued and then covered with the Gillespie Borate version.
But wait, there’s still more fun to be had, but first I must warn you, it’s a little bit bad. (wow, I’m starting to feel like the Cat in the Hat…) Two words – Ferric Chloride. It is a hazardous material, so do take precautions – proper safety equipment should be worn when handling and using. That said, it is a lot of fun with which to experiment. At right is a piece glazed with the gerstley clear, then sprayed with ferric chloride and reduced in sawdust. In this case, the ferric chloride fumes to many parts of the pot, rather than just where it was sprayed. At left is a piece pulled from the kiln, sprayed with ferric chloride and immediately quenched in water. This provides a much more localized fuming of the ferric chloride. (Note: The solution we used is comprised of Lump Reagent Ferric Chloride dissolved in water. If you are interested in this process and need help obtaining the proper materials, let us know)
“I like to [Raku], oh I like it a lot, said the cat in the hat to the fish in the pot…I will not go away, I do not wish to go, so I’ll show you another good trick that I know”
Now we can have some fun with stains, one of my mother’s favourite things. Using any metallic oxide and mixing with equal parts bentonite and borax (dissolve borax in hot water first, then add the mixture of bentonite and oxide to the borax/water mixture), you can make a wonderful stain (useful beyond Raku, by the way). We mixed up 7 stains. Because Copper often fumes onto other things, the copper stain was tested separately from the rest, which are shown below. All stains were covered with the gerstley borate clear. Red Iron stain is not shown because, well, under the clear it simply acts as a flux and completely loses all color. Also of note is that we substituted Mason Stain 6404, Vanadium for Vanadium Pentoxide, which is highly toxic and nigh impossible to find. And no rule would be complete without an exception, so I need to point out that when using Cobalt, only 1/4 part should be used.
We did a couple other tests with stains mixed up under clear. At left is a piece in which a different stain was applied to each different texture. Now, it is my policy to show the good, the bad and the ugly in my glaze of the month tests. This would be a good example of something going terribly awry. You may or may not know that Kansas is EXTREMELY humid in the summer. This means that it takes glazes an achingly long time to dry. That coupled with the fact that I’m not exactly known for my patience = the glaze was not completely dry when I started to fire. As the glaze dried from the heat of the kiln, it cracked and pieces flaked off, leaving bare spots on the piece. In some places the remaining glaze ran a little bit and got thick and milky.
However, in a way, it was a happy accident in that enough of the glaze flaked off where the iron oxide stain was for me to see that colour, and I also found that I really liked the chrome stain without clear. So, this led to the bottle on the right, which is the chrome, cobalt and vanadium stains brushed on the bottle and red iron stain around the neck and lip. Then just a few swats of clear were applied for contrast.
You may think that’s all, but wait, there is more. I will show you a trick with some Copper Carbonate…oh shucks, that doesn’t rhyme. Guess I should leave that to Dr. Seuss after all, and I’ll stick to glazes.
Our crackle white glaze also works well as a base in which to add additional ingredients. Copper is always fun to start with, so for a great copper gloss, try adding 10% Copper Carb by weight to our crackle white. The heavier the reduction, the more copper penny results you will have. My personal taste leans more toward iridescence and shimmery-ness than bright metallics, so I did not do much reducing, and we achieved this beautiful teal colour with hints of silver. I suppose it’s only right for me to reveal that we were not using the regular copper carb that we sell. For this, mom pulled out “the good stuff”: A very limited supply of reagent grade copper carbonate that comes in 1 pound jars. I think mom has about 10 of them left. If you REALLY want some and live close enough to visit in person, she *might* be willing to part with a few of them. I also like Copper Matte Raku glazes a lot. So, here’s one for you to try at home, again using our Crackle white as a base. 5 parts crackle white, 4 parts bone ash (DiCalcium Phosphate, or “natural” bone ash), 2 parts Copper Carb. One of the tricks to a good copper matte is firing it properly. They’re a bit more finnicky than most raku glazes. The image at the right is perhaps slightly underfired, but the colours are luscious. You can bet I’ll be doing more work with this one!
So there’s a starting place for you, but you certainly don’t have to start there. Stretch your mind and try some new things with Crackle White! Now is the perfect time to pick up a bag, regularly $1.55 per pound,