Min

+1
Linda Arbuckle quote below regarding glaze calculation that I think pretty much sums it up for me:
"The purpose of glaze calculation is to determine the total amount of each element present in a glaze, and the proportions relative to each other. With that information at hand, it is possible to calculate materials substitutions, revise melting points, and do other useful calculations. In the end, testing is the final proof, but unity molecular formula gives you a more informed method of choosing what to test."
Are there qualifiers to interpreting the figures with glaze calc, yes of course there are. 
Glaze calc is another tool in the toolbox, one that can save a lot of work and material waste. I also use Limit / Target Charts, they aren't written in stone either but combined with UMF they can be a pretty good indicator if a glaze is worth mixing up and testing. An overload of boron, for example, might make a pretty and interactive glaze but I do question it's durability. Lots of lithium, I'm going to be wary of shivering. High level of sodium and / or potassium, odds of crazing are going to increase. Low alumina and / silica, glaze is not going to be durable regardless of flux ratio.  And so forth.  
Recently there have been a few materials that have become unavailable to potters, Custer, Gerstley Borate, some talcs plus the EPK shortage. Looking at the UMF for any of these offers a way to find alternative materials and or a combination of materials that can be used in place of ones lost and bypass a lot of the trial and error testing.
 
 
 

And here we come to it, the rub. 
Glazy has been a godsend to me, and I’ve yet to see anything bursting that bubble. I learned glaze chemistry and calculation thirty years ago in college, and used it loosely, only to evaluate recipes. Now, as then, I rely heavily on materials knowledge and gross ratios to come up with what I believe will work. Glazy allows me to put my guesses into a context of what has worked in other places for other people, and reduces (not eliminates) the testing. For materials that don’t have a published chemical analysis, or materials that have the same name but varying compositions (this talc vs. that talc, “ potash spar,” “boron frit,” or my local clay) there’s still guesswork. 
It takes much less effort to arrive at a data point that before would have been tedious to find, even with previous glaze calculation software. Glazy rests on the shoulders of everything that came before it and I don’t discount that, but we live in good times. Three cheers for Derek Au. 
I, like @Roberta12, look for that sweet spot on the UMF chart, nudge my glazes towards it and wait and see how the pots look after a few years in my kitchen. The only faster way to test seems to be alternating baths in strong alkali and acid (good old lye and that potent 30% vinegar @PeterH mentioned in another post). Like the weatherman, we haven’t arrived at perfect prediction, but it’s a lot better than it used to be. 

I just had to find the full document: https://aura.alfred.edu/server/api/core/bitstreams/182c2504-e6ac-42f7-bb12-34492c950d5f/content
 

+1
Linda Arbuckle quote below regarding glaze calculation that I think pretty much sums it up for me:
"The purpose of glaze calculation is to determine the total amount of each element present in a glaze, and the proportions relative to each other. With that information at hand, it is possible to calculate materials substitutions, revise melting points, and do other useful calculations. In the end, testing is the final proof, but unity molecular formula gives you a more informed method of choosing what to test."
Are there qualifiers to interpreting the figures with glaze calc, yes of course there are. 
Glaze calc is another tool in the toolbox, one that can save a lot of work and material waste. I also use Limit / Target Charts, they aren't written in stone either but combined with UMF they can be a pretty good indicator if a glaze is worth mixing up and testing. An overload of boron, for example, might make a pretty and interactive glaze but I do question it's durability. Lots of lithium, I'm going to be wary of shivering. High level of sodium and / or potassium, odds of crazing are going to increase. Low alumina and / silica, glaze is not going to be durable regardless of flux ratio.  And so forth.  
Recently there have been a few materials that have become unavailable to potters, Custer, Gerstley Borate, some talcs plus the EPK shortage. Looking at the UMF for any of these offers a way to find alternative materials and or a combination of materials that can be used in place of ones lost and bypass a lot of the trial and error testing.
 
 
 

+1
Linda Arbuckle quote below regarding glaze calculation that I think pretty much sums it up for me:
"The purpose of glaze calculation is to determine the total amount of each element present in a glaze, and the proportions relative to each other. With that information at hand, it is possible to calculate materials substitutions, revise melting points, and do other useful calculations. In the end, testing is the final proof, but unity molecular formula gives you a more informed method of choosing what to test."
Are there qualifiers to interpreting the figures with glaze calc, yes of course there are. 
Glaze calc is another tool in the toolbox, one that can save a lot of work and material waste. I also use Limit / Target Charts, they aren't written in stone either but combined with UMF they can be a pretty good indicator if a glaze is worth mixing up and testing. An overload of boron, for example, might make a pretty and interactive glaze but I do question it's durability. Lots of lithium, I'm going to be wary of shivering. High level of sodium and / or potassium, odds of crazing are going to increase. Low alumina and / silica, glaze is not going to be durable regardless of flux ratio.  And so forth.  
Recently there have been a few materials that have become unavailable to potters, Custer, Gerstley Borate, some talcs plus the EPK shortage. Looking at the UMF for any of these offers a way to find alternative materials and or a combination of materials that can be used in place of ones lost and bypass a lot of the trial and error testing.
 
 
 

20 oz mug, 1 lb  (base isn't as narrow as it looks in the picture)

Blue shades of stains don't use Cd (cadmium), cobalt is commonly found in blue stains (or vanadium for turquoise shades). For many yellows, oranges, pinks, reds and some purples a cadmium inclusion stain is used to supply the colour. 
More about Cd inclusion aka encapsulated stains here if you wish to learn more about them.

Hard to argue with that, but I would suggest that they can help reduce the number of tests you need to make.
For glazes that phase-separate (e.g. many mattes) the UML formula will not accurately reflect the composition of the different phases.  Which raises issues of interpretation and limit setting.

thank you,  madeleine,
your picture of the printer's blanket is just what i have wanted to do for years.   posting pictures is so complicated now, that i have not even tried.  windows 7 was easy.  i am now up to windows 11 and i do not even want to try.
rae, if you just call any large printer and ask them if they use printer's blankets they will tell you.   some smaller blankets are used by smaller companies so ask if they do city size newspapers.  all the blankets i have used came from big city newspaper printers and were the size of an open newspaper.  i am sure that los angeles has at least one big newspaper.  ask them the name of their printer.
i cut them so they will fit on my 24 inch bailey slab roller so i  usually get a top and a bottom out of one 48inch wide blanket.  the printer uses the blue side and sometimes it is not totally clean.   ask what they use to remove the ink.  i think i remember fingernail polish remover working.
hulk, can you identify the shelf "paper" you use?   around here people call the brand called "Conctact" which is actually plastic, not paper, "shelf paper".   i am sure mentioning a brand name here is not forbidden.
 

Printers blanket, top side is the cream colour and has a very fine texture, much less than the canvas usually used for slab rollers. Bottom side is blue rubber material. Another advantage of using these is they don't bunch up like can happen with canvas sometimes when starting to put it through the rollers.

20 oz mug, 1 lb  (base isn't as narrow as it looks in the picture)

20 oz mug, 1 lb  (base isn't as narrow as it looks in the picture)

Well at this point you may be right but I am trying to be nice to a man in his 80s, could have who knows what health issues going on, and overwhelmed with a backlog of orders. Yes, at this point I am taking the polite hat off now that we know a bit more, but I figured that would be my initial approach. 

20 oz mug, 1 lb  (base isn't as narrow as it looks in the picture)

20 oz mug, 1 lb  (base isn't as narrow as it looks in the picture)

Printers blanket, top side is the cream colour and has a very fine texture, much less than the canvas usually used for slab rollers. Bottom side is blue rubber material. Another advantage of using these is they don't bunch up like can happen with canvas sometimes when starting to put it through the rollers.

Not to worry, folks have made glazes forever and experimented looking for predictable ways to characterize what happens. They publish their findings or research and you get to decide if it is useful to you. Commercial glazes have the issue of - what is in them and how does one correct a defect such as crazing. The good part is commercial glazes don’t use lead anymore (for the most part), vanadium pentoxide etc… generally because someone found out it was a bad thing. If you mix your own then you know what is in it and can reasonably test for durability, fit, etc…. to your satisfaction, before selling it or giving it as a present for human consumption. I think it does help to inform but definitely not for everyone.

Link here on how to determine if your clay is suitable for outdoor work that undergoes freeze and thaw cycles. https://community.ceramicartsdaily.org/topic/23472-frostproof/
Link here on one method of glaze fit testing. https://digitalfire.com/test/bwiw#:~:text=-Select samples (or shards),ice water for three minutes.

Good example of how layering 2 dissimilar glazes can often result in very interesting glaze effects.

With all due respect, I think sometimes being too polite doesn't work with some people. Why are you saying sorry to him? 

Finally a date!  Thurs Feb. 8 on CBC and CBC GEM.  Lin

I would put some spar in the recipe plus some 200 mesh silica. Although, if this is a one time firing and you haven't tested a woodfire body before I would be inclined to purchase a claybody and wedge in your inclusions. I would ask the people firing the kiln which claybody they recommend and if they are okay with you adding decomposed granite or whatever you are thinking of adding that isn't an organic material.

I would put some spar in the recipe plus some 200 mesh silica. Although, if this is a one time firing and you haven't tested a woodfire body before I would be inclined to purchase a claybody and wedge in your inclusions. I would ask the people firing the kiln which claybody they recommend and if they are okay with you adding decomposed granite or whatever you are thinking of adding that isn't an organic material.

I would put some spar in the recipe plus some 200 mesh silica. Although, if this is a one time firing and you haven't tested a woodfire body before I would be inclined to purchase a claybody and wedge in your inclusions. I would ask the people firing the kiln which claybody they recommend and if they are okay with you adding decomposed granite or whatever you are thinking of adding that isn't an organic material.

Katz himself might have thrown a wrench in the works in regards to his testing into flux ratios, also into further exploration into silica:alumina flux ratios. From his 2016 NCECA presentation taken from this pdf.