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Batch Recipes / A sample of colorants for SP87
« Last post by Administrator on January 25, 2019, 09:41:47 PM »
Here's a simple paste from a document obtained from Craftweb which seems to use SP87 batch or color base as a starting material. I have not used these! Some of these chemicals are toxic. USE WITH EXTREME CARE.

The original word document is attached for convenience.

Glass recipes
Crystal Colors
Transparent Yellow
19 lbs color base
*40 gr. cadmium sulfide
25 gr. selenium
*20 gr. sulfur
70 gr. potash
*90 gr. soda ash

Transparent Amber
19 lbs color base   (you may deepen this color by increasing the sulfur up to 80 gr.)
*40 gr. sulfur
*5 gr. sugar
*85 gr. soda ash

Transparent Red / striking color
19lbs color base
*80 gr. cadmium sulfide
40 gr. selenium
*400 gr. zinc oxide
100 gr. potash
*65 gr. soda ash

20lb Pellets
350g Manganese dioxide
90g black iron oxide

Transparent Violet
19 lb color base
160g manganese dioxide
6g cobalt carbonate
*85g soda ash

Transparent Green /Yellow
19lb color base
*20g potassium dichromate
*85g soda ash

* You must screen or sift these ingredients to get rid of lumps
Transparent Dark Green
19lb color base
120g  potassium dichromate
100g black copper oxide
85g soda ash

Transparent Cobalt Blue
20lb batch pellets
55g cobalt carbonate
*10g soda ash

Transparent Green
19lb color base
40g potassium dichromate
8g copper carbonate
*85g soda ash

Transparent Aqua
19lb color base
40g potassium dichromate
110g black copper oxide
*90g soda ash

Transparent Royal Blue
20lb color base
12g black nickel oxide
80g copper carbonate
20g cobalt carbonate
*75g soda ash

Transparent Copper Blue
19lb color base
100g black copper oxide

   You must screen or sift these ingredients to get rid of lumps

19lb color base
220g manganese dioxide
20g cobalt carbonate
112g black nickel oxide
*130g soda ash

19lb color base
112g  black nickel oxide
220g  manganese dioxide
20g cobalt carbonate
*65g alumina hydrate
*65g soda ash

Transparent Grey
19lb color base
10g black nickel oxide
.5g cobalt oxide

   You must screen or sift these ingredients to get rid of lumps

Opal Colors

Opal White/striking
19lb color base
*570g STP
570g boric acid
*600g silica flour
19lb color base
470g STP
470g boric acid
560g silica

Opal Yellow / striking color
18lb color base
*40g cadmium sulfide
25g selenium
*20g sulfur
*650g zinc oxide
70g potash
*90g soda ash

Opal Orange
18 lb color base
40g selenium
*40g cadmium
20g sulfur
*650g zinc oxide
70g potash
*90g soda ash

Opal Green
19lb color base
470g STP
470g boric acid
560g silica
10g black copper oxide
45g potassium dichromate

Opal Light Sky Blue
19lb color base
*470g STP
470g boric acid
*560g silica
70g black copper oxide

Opal Lapis
19lb color base
*470g STP
470g boric acid
*520 silica
55g cobalt carbonate

Opal Blue
19lb color base
*570g STP
570g boric acid
*600g silica
12g black nickel oxide
40g copper carbonate
10g cobalt carbonate

* You must screen or sift these ingredients to get rid of lumps
Tools / Compatibility Testing: Ring test
« Last post by Administrator on January 25, 2019, 07:34:23 PM »
I really like the ring test. You apply a stress to the glass and see if it can take it. I make a cylinder large enough to allow a few rings to be cut out of it. It can be a thick ring test or a thin ring based (I think) on the types of final glass you will be making. I make the thicker type with walls around 1/4"-1/2" thick. I've got a large 14" tile saw and just make rings starting from the center of the cylinder. Making a single ring from the top is kind of cheating and doesn't mean an "internal" ring will survive.

When a ring makes it you can slice it to see if it has much stress built up. If it closes a bit, the outer layer has a higher LEC than the inner layer. You need to make both an encased and outside version of your test glasses to be sure they are fully compatible. I have an opal phos which works when it is on the outside, but cracked immediately on the saw when encased.  >:(
Tools / Glass Calculator
« Last post by Administrator on January 25, 2019, 06:46:44 PM »
Attached is an excel file for a batching calculator originally made by Dave Bross. I've included, as an example, a copy of the glass formula Pete has accused me of stealing. It is however, derived from a formula posted on Craftweb.

Silica 47.42 lbs
Soda Ash 15.21
Lime Hydrate 6.78
Potassium Carb 3.94
Borax 5 mole 1.65
Pot nitrate 150 Grams
Antimony tri Ox 75 grams

An issue with this formula is durability as it lacks alumina. A good number to shoot for in alumina is 1% or greater. The Nick Labino rule would have this greater than 2%, but this becomes rather stiff and difficult to work with. Adding some custer feldspar allows easy melting, added potassium and our alumina content. This is the final clear glass which can be made an unoxidized color base by removing the potassium nitrate and antimony...simple!

I will refer to the features in the calculator in all my projects posts. In addition to Dave's original E&T numbers for LEC, the calculator includes another set of coefficents to calculate the expansion completely differently (Other Exp). This glass as made is a very good match to other "96 COE" glasses. Therefore, it would seem that the "Other Exp" numbers have a decided edge in predicting a 96 LEC glass. I also added pricing based on some raw material sources like Seattle Pottery and US Pigments.

As Dave says...use, distribute and improve!
Projects / Opal Phosphate Batch
« Last post by Administrator on January 25, 2019, 06:10:05 PM »
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 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

General Discussion / Welcome
« Last post by DanielJanse on January 25, 2019, 05:27:11 PM »
Well, I did it. Finally got myself banned from Craftweb. I figure if I have 6 months without access to it I might as well see if I can start a new, better community. I've seen names on the posting board come and go. Wondered what happened to a lot of those folks. Seemed like they asked reasonable questions and had plenty of experience but Pete's not much for those second guessing his opinion or even worse just having one of their own. 

I won't dwell on that too much. I'm hoping we can build something better. A place for glass artists to come and share their opinions, questions, concerns...whatever. Most of all, I'd like a better place to learn and share.

Here's a list of differences between the 2 forums:
- No names required, guests allowed.
- You will not be ridiculed for asking a question.
- Larger picture files and uploads.
- New format...latest and fully functional interface.

To that end, my first project posting is a current effort to make a variety of Opal Phosphate glasses. I am indebted to Dave Bross and Jordan Kube to sharing their experiences on Craftweb. Also, the recent posting from Lynn Read on SP87 used in making a Opal Phos...very interesting stuff.
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