A significant change has been made in the G-200 Feldspar. If you are using
this product you will need to make some adjustments to your clay & glaze
formulas. The new G-200HP will be higher in potassium and alkali levels. The
reason for the change is a decision by Imerys Ceramics to stop blending feldspar
from two different deposits. For some time now the Feldspar Corporation has been
blending their Sodium Feldspar from Spruce pine, NC with their Potassium
Feldspar from Monticello, GA. This was done in effort to keep the same published
levels of sodium and potassium as they had in a mine that is now depleted.
Imerys Ceramics is recommending to their customers to blend 28-30 % of sodium
feldspar to the new G-200HP feldspar. (7 Parts to 3 Parts) If you are buying
prepared clays or glazes from Sheffield Pottery this will be done for you. If
you are mixing your own, you will need to blend the G-200HP with Minspar 200 or
Kona F4 Feldspar. Both are mined in Spruce pine, NC and have almost identical
chemical properties. We are currently using the Kona F4 but will be switching to
Minspar 200 as the Kona F4 mine is closing.
You may still be able to use the new G-200HP without blending in some
formulas but you should definitely do proper testing first.