A little history...opal phosphate (
Milk Glass) became interesting to me as a non- or less toxic means of achieving an opaque glass color. Since I started using enamel white I always wanted a tank to just gather a nice layer of color-contrasting white. Opal phos seems a great option for this, but it does have some drawbacks.
Opal phos can be made very dense by increasing the phosphate % and can be white drawn from the pot. However, the more phosphate the harder it is to melt. It's a little bit textured, as is, so anything that resists melting is going to make it worse. When the phosphate level is made more moderate, the phosphate strikes white as the glass cools. Heating and cooling increases the density of the white. Why? Tiny phosphate gas bubbles are formed which block light transmission. More cycles= more bubbles. Wow, right? Another issue: it is very hard to predict its compatibility in a batch calculator. Gotta test and test and test. I also wonder if the expansion changes based on the degree of striking...it gets more stiff so chances are it does.
So, I've been working with Dave Bross' formula which he formulated for electric element furnace melting. Works very nicely but I wanted it to match Cristalica cullet. Took a while but I got it matched with a theoretical LEC of 87. Now, I am trying to modify the formula to use feldspar (custer) instead of alumina hydrate. I'm also lowering the alumina to soften it up a bit and help the melt.
Future modifications for the glass will be:
- reddish tint with Black Tin
- silver-luster opal phosphate (reduced glass body/black tin)
- colors of opal phosphate (blue, purple, green, jade, red)
- Chalcedony/opal phos fusion.
Another reason for moving to a new base glass slightly different from Dave's original was to remove the nitrate. This should help in overcoming the oxidizing properties of the glass and with the help of black tin...make it neutral or reducing.
More to come...I'm actually waiting for the cryolite to arrive in the mail.
About the attachment. This is from a great website built for glaze recipe record-keeping. Lots of features I've yet to use yet but I'd been looking for a way to add comments to batches and help in making tickets to take to the batch room. It's cheap, feature-rich and easy to use. It's a user side to a public information website called digital-fire.com.
www.insight-live.com