Dave Finkelnburg on fri 2 jan 04
superphosphate
Like Logan Oplinger, I have also used superphosphate fertilizer as a direct
substitute for bone ash in glazes. It works very well! It is calcium
phosphate in about the same percentages of calcium and phosphorous as found
in bone ash.
The only reason I have more recently quit using the inexpensive and
readily available triple superphosphate is because sometimes the fertilizer
contains residual phosphoric acid from the manufacturing process. The acid
reacting with limestone in my glaze releases carbon dioxide that causes the
glaze to foam on mixing. Naturally, the acid also flocculates the glaze a
bit, which isn't bad. It takes an extra-large container to deal with the
volume of foam and time to wait for the reaction to go to completion and the
foaming to cease.
Now I just buy bone ash from Laguna through my supplier. Laguna lists
bone ash in their catalog at under 50 cents/pound in 50-pound bags FOB
either City of Industry, CA or Byesville, OH.
Good glazing!
Dave Finkelnburg
----- Original Message -----
From: "Logan Oplinger"
Sent: Thursday, January 01, 2004 11:17 PM
> If you can't get bone ash from your pottery supplier, try your nearest
> agricultural/garden supply store. Ask for super or triple super phosphate.
> These are SOLUBLE forms of calcium phosphate, but may work for you.
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