Feldspar

[Norm Stuart]

Before I run out of old bags of discontinued glaze ingredients, does anyone have any mix ratios for Kona-F4 feldspar or Custer Feldspar?

.

Digitalfire recommends using:

Minspar-200 to replace Kona-F4 which is similar;

a mix of 30% Minspar 200 and 70% G200-HP to replace G-200 old, which is also similar to Custer.

.

Should I stock just Minspar-200 soda and G200-HP potash feldspars and rewrite my recipes, or is there a visible end difference with Custer feldspar which makes it worth stocking as a third feldspar?

Will I see a difference replacing Kona-F4 with Minspar-200? Obviously I learn this the hard way, but any experience would be appreciated.

On the topic of Iron Oxide, the metal oxides made with the Bayer patent method for high purity red iron and other iron color pigments, with or without and chrome pigments are marketed wholesale as Laxness - Bayferrox® and Colortherm®.

My understanding is this red iron oxide is more pure than the sulfate containing red iron oxide produced by the prior method owned by Cities Service and Mapico, which may be what is sold as Crocus Martis. Although I notice NMClay sells Bayferrox 180 as a Crocus Martis replacment - kudos to them for identifying what they're selling.

"Red iron oxide precipitate" from Standard Ceramic and "red iron oxide special" from US Pigment look slightly different but could be the same item as they seem to fire about the same.

.

http://www.bayferrox.us/product_information/docs/Colortherm%20Broch...

http://bayferrox.com/en/products-applications-bfx/colors/

Bayer - http://www.google.com/patents/US3946103

Mapico - http://www.google.com/patents/US4256723

[George Lewter]

I stock Custer because it seems to be the most often used of the feldspars, and has been for many years in the US, hence a great number of existing recipes call for it. As Tony reported, the manufacturer, Pacer, claims it's composition has not changed significantly in 50 years. They have an analysis dated 2005, indicating 10% potash and 3% soda. Ron Roy reports a decline in the potash content over time to about 7%. This is significant, and to be watched, but not in my opinion enough to rework every recipe calling for Custer, unless new problems are occurring. G200-HP is about 20% more expensive than Custer where I am.

If I ran into a crazing problem with a glaze using Custer Spar, partial or full substitution with G200-HP might be a solution, as I would be diminishing and replacing higher expansion soda with lower expansion potash of otherwise similar fluxing power and effects in the glaze melt.     

 

[Norm Stuart]

I guess that makes sense to continue stocking a bag of Custer feldspar for convenience. G200-HP is 25% more for us.

Each fifty pound bag cost us (two months ago, plus 8.75% sales tax):

$15.05 for Minspar soda-spar;

$16.00 for Custer;

$20.02 for G200-HP potash-spar, or for Laguna's G200-old blend;

$31.50 for Laguna Gerstley Borate;

$17.67 for A-400 Nepheline Syenite;

$15.75 for Vansil W-30 Wollastonite;

(it's tough putting wollastonite through the sieve, there's a silane-treated Vansil W-50 with a 50% smaller particle size used in the plastics industry, but Laguna doesn't stock it. I wish I knew a way around this)

$15.19 for Silica-325, or $32.00 for Imsil A-25;

$11.50 for Dolowhite-select-200 Dolomite;

$11.40 for Ball Clay OM4.

Frits are of course more costly, ranging from $65.50 for Ferro 3134 up to $70.91 for Ferro 3269, and $101.00 for Ferro 5301. 

Ferro frit 3249 (anti-craze) used in Tony Hansen's G1215U - Low Expansion Glossy Clear is an outlier at $184.44 due to the costly magnesium.

I think Laguna includes feldspars, kaolins and ball clays in our clay volume discount, depending on our order size. We also have to tack on 8.75% for California sales tax.

Laguna's price to us is always somewhat lower than their posted prices on their Florida Axner website, but by a seemingly random percentage. Laguna doesn't provide posted prices. We have to email or fax them a list to receive a price quote good for 30 days to find out what the price will be.