Glass Calculator

[Administrator]

Attached is an excel file for a batching calculator originally made by Dave Bross.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. http://talk.craftweb.com/showthread.php?t=7288

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!

[vitroholic]

I loaded up the calculator and fooled around with it a little.
I haven't done batch calculations since college, back when computer time wasn't easy to come by. I remember thinking it'd be cool to get the calculations put into my brother's programmable calculator to streamline the process, but of course I never did it. 
Still, Dave's calculator looks nice, and being open source helps with someone like me who isn't going to make any money off of my work for some time to come, if at all.
A couple of questions, though.
there's a lot of colorants left out of the tables. How hard would it be for a dope like me to add them?
I'm going to start out using SPB color base. I got the stuff so long ago, I have little info on what's in it. Without stepping on any large and sore toes, I wonder if there'd be a way to insert this formula in there? Maybe the batch calculator is something better to use with a fresh formula, or the one dave so helpfully included with the spreadsheet.
I'm still working from theory on all this, as I have to build a barn to house my studio before I can start melting anything.
If only the ground would dry up a little so I can start the foundation.
Still, I can start gathering up the knowledge and practice with formulation in the meantime

[Administrator]

The formula in that calculator should not be attributed to Dave...that's my doing. It's a Vanderlaan formula that has been published on Craftweb save the alumina. I think it's a great starting point to make your own custom batch or as is. Add lithium if you want more working time. Remove borax and replace with KNO₃ if you don't like it's corrosive effects. Test, test, test.

Glad you got a chance to play with this calculator. It's got a few modifications made by me and you wonder if they will be clear for others to use. The colorants are mostly metal oxides and expansion coefficient numbers for those in glass are lacking. Lots of people have used the numbers from a study performed on glass enamels which doesn't estimate their properties in glass effectively. The good thing is that these metals are typically used at such low percentages that any effects on expansion can be ignored or corrected easily. Check out the SP87 color base batch listing I posted...whole list of recipes for a bunch of colors to achieve with this batch. The opal phosphates also include extra sand in the recipes to overcome the effect of the phosphate. Problem with them is that they use bone ash which in its early form is hard to come by. In other words, the stuff they sell today just ain't the same. Worth a try though, but a better phosphate choice is sodium tripolyphosphate (STP, or STPP). The fluorine content in SP87 is very helpful in making this batch melt effectively as an opal phos.
I also put up a calculator for a theoretical SP87 which was made using a published analysis of this batch. I'll need to tweak it a bit after I read up on a few posts describing the SP87 color base. In it is discussed the specific things that were removed from the batch for the color base. Remember to mix the contents of the bag very well before starting. It is NOT mixed...they drop the ingredients right in the bag. It will ruin the whole bag if 10 lbs are taken out to test only to realize that the batch wasn't mixed effectively. If I sound like this is currently an issue for me, you're correct!