|Monthly Tech-Tip |
Modified: 2013-03-25 08:47:26
High Boron, Opaque Cone 6-10 glaze
|Ferro Frit 3110||50.00|
Purpose: To obtain greater firing range and more "flowery" crystals by the addition of extra boron and calcium.
Tony Hansen gave me the idea to try a higher boron glaze in order to get the peak temperature down to something that wouldn't be so hard on one's elements. I thought D8-9 would be a good target since it doesn't supremely stress the elements but still allows most porcelain bodies to mature. The boron level in this glaze is actually quite low compared to many other (non-crystalline) glazes, but the effect of even this little bit of boron and calcium is exactly what I had in mind.
Bory 1 is a base I made up simply as a test, and it has now surpassed the old Octal (see the first edition or the Crystalline Ceramics Web Resource) on my list of favorites. It's so straightforward and dependable that it's my base of choice for workshops. Since coming up with this recipe, Bory 1, I've tried eight slight revisions. But in this case, the original is still the best. I did make a lower titanium version which was quite nice too, by lowering the titanium dioxide to 3% and upping the zinc, frit, silica and borate by 1/2% each. It works very well and gives lovely copper turquoises.)
I've tried this glaze with both the new synthetic borates and with Gerstley Borate, and found the old standard the best for my purposes, since it gives me the brightest and purest colors.
Bory 1 produces crystals in profusion, but only rarely does it cover a surface completely with crystals. So if you prefer to see a lot of ground, this is a good glaze for you. As often happens, it will felt up with additions of cobalt, and occasionally with copper, so I suggest not going over 2.5% cobalt carbonate or 2% cobalt oxide and adding 0.5% vanadium or rare earth oxide (of your choice) to prevent felting.
Bory 1 and nickel - either carbonate or oxide - are not a match, due to Bory's high titania content. But you will get some good results with the transparent-ground version mentioned above.
So far as I can tell, mixed Bory has a decently long shelf life (over six months though I've never used any beyond that; I always run out first). I've fired Bory 1 as low as D6 and gotten some nice crystals; however, at D5, you'll need to seed the crystals, as they won't form on their own.
To use Bory at D6, fire to 1221C, hold there for 20 minutes, cool slowly to about 1070C, and then hold anywhere between 1010° and 1140°. You will find much less variation in crystal shapes at D6 than you will at D9 (actually, this is true of just about all these glazes).
One point I should mention is that Bory is quite soft. It is very easily scratched so probably not a good glaze for any object that is going to be well handled.
The firing schedule provided with yield broad, flat crystals which show two rings of different shades. The inner ring, formed at a higher temperature, will be darker than the body of the crystal; the other ring, formed at a cooler temperature, will be a lighter shade. The effect is best seen with cobalt and iron colorants. Nickel should not be used with this amount of titanium or a sickly green will result.
Bory 1 Fara Shimbo Crystalline Glaze
Eight-step firing to 2012F
Shimbo Crystal Holding Pattern 3
Electric firing: Crystal Glazes 2 by Fara Shimbo (page 139)
Crystalline Glaze Recipe Fara Shimbo
These are from Fara\'s Crystal Glazes book II.
A type of ceramic glaze made by potters. Giant multicolored crystals grown on a super gloss low alumina glaze by controlling multiple holds and soaks during cooling
|Crystal Glaze Variations||Addition of boron via Gerstley Borate produces broad, flat crystal fans. (Any borate can be used if Gerstley is not available.)|
|Glaze Color||Crystals will be more yellowish than the ground, which is generally a soft white when no colorants are used. Cobalt used in this glaze yields blue crystals on a mustard-colored ground; copper crystals and ground shaded toward light grass green.|
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