How to approach thickening caused by CMC or MAGMA additive

[Beebop]

I have follow-up questions based in recommendations from my previous post. I’m looking into MAGMA and CMC additives to improve the working properties for some of my glazes. I see that both thicken a glaze. Since the glaze+additive goes on thicker, does this cause a thicker glaze layers in the fired product? Or is the thickness entirely due to the organic that burns off, and it leaves behind roughly the same amount of glaze after firing? Should I be trying to dip quicker or brush fewer layers since the glaze is thicker, or apply as normal because glaze thickness is just not the equivalent when compared to a glaze without additive? Thanks the all the help, I learn so much each time I post I really don’t think I could be a glaze maker without this forum!

[Mark C.]

I use magma to float glazes-it does not stink or go bad like CMC gums do. I have used gums a bit until I found Magma abiout 20 years ago. I adjust specific gravity of glaze than add the magma. I use it in high fire glaze so brushing is not what I do much of-usually dipping or pouring. The glaze may appear thicker  but its the right specific gravity so it fires our fine. I only use it in a few glazes that settle like bricks. I apply that glaze the same as all others and do not try to overthink it,

In this old post I explain how to prepare and store it

one other note-Mins use of the syringe is faster is a understatement-I bought two 100m syringes and use them every week-wow a real time saver-Thanks Min for that tip

 

Edited July 30, 2022 by Mark C.

[Min]

+1 to what Mark said, get the sg right then add the least amount of either Magma or CMC you need then just get used to working with a glaze that looks thicker. Much the same as if you add Epsom salts to a glaze. Think of it like adding a cornstarch slurry to a sauce or gravy, it will thicken it but hasn’t increased the concentration of the sauce.

If you do use either Magma or CMC be sure to add a tiny amount of copper carb to act as a preservative, it will work with either. Since both products are organic it stops them  rotting if the glaze isn’t used up quickly. On paper both products work, I prefer how the glaze dips with Magma so have stopped using CMC. I wouldn’t use it if the crawling is due to using 2 high clay content glazes and you are layering those glazes, for those glazes I would calcine part of the clay. Magma also  let’s you layer glazes without them lifting / peeling while drying as some glazes do, especially if they are applied when the base glaze is too dry.

[ATauer]

CMC definitely burns off! It is methylcellulose, so glue basically made from the fibers in trees.  The way I use it I usually don’t put it in a big 5 gallon bucket of glaze because it can rot, I remove a portion of glaze that I am planning on using soon and add the CMC just to that, that way it won’t rot. But it doesn’t help your 5 gallon bucket of glaze, unless when you add CMC to it you add a pinch of copper carbonate. I learned that on Glazy from a real super star of a glaze maker/inventor, and it makes tons of sense to me because I use 0.2% per dry weight of cu carb mixed with my paperclay to keep it from growing mold and the cellulose in it breaking down, and it works so well the clay will last for at least two years. I don’t think anyone has left the clay longer than that to see how long it could really go. It is used interestingly enough in antimicrobial cleaners in baby wards in hospitals for its antimicrobial/anti mold properties, while having an extremely low risk of toxicity of any kind. Been used like that for decades if not longer, so it legit will keep your CMC from rotting the glaze without having really any toxicity issues you need to worry about unless you drink your glaze, and even then I happen to know the dose would be too low to give you any symptoms! I know a pinch is rather hard to measure! You want enough to prevent rotting in the glaze without adding color or fluxing the glaze. You kind of have to play around a little to know how much that is, but around a 1/2 teaspoon to 5 gallons of glaze often works. There are other variables, like the weather, humidity, heat levels etc where you keep your glazes in how much it will want to grow bad stuff, so you may have to play around with the amount. And CMC in powder form is quite cheap, cheaper than anything else I’ve seen for the problems it treats. 

Just randomly, as I know you’ve said some of your glazes get cracks in them on the bisque and some of those types of issues, another thing you can do to help with that is use Karo syrup in the glaze (only the amount you are going to apply) and it is so sticky that it seals the glaze to the bisque and makes issues like that disappear. It often makes brushing on glazes much easier as well if you need to do that and your glaze is formulated for dipping. Which brings me to a thought I’ve had about your glazes, and adding binders and stuff- making sure you know the difference between a dipping glaze and a base coat dipping glaze, and make sure you are aware of which one you are making, and how that effects application and firing and flaws…this is especially important if you are dipping more than once, or layering. Two great links on the differences between the two and what you need to do and what to look out for…it may be that some of the problems you are having is you are using one when you should be using the other…

https://digitalfire.com/glossary/base-coat+dipping+glaze

https://digitalfire.com/glossary/dipping+glaze

Edited July 30, 2022 by ATauer

[Min]

1 hour ago, ATauer said:

will keep your CMC from rotting the glaze without having really any toxicity issues you need to worry about unless you drink your glaze, and even then I happen to know the dose would be too low to give you any symptoms! I know a pinch is rather hard to measure! You want enough to prevent rotting in the glaze without adding color or fluxing the glaze. You kind of have to play around a little to know how much that is, but around a 1/2 teaspoon to 5 gallons of glaze often works

What works with CMC is 1 US gallon of very hot tap water with 1/4 teaspoon copper carb plus 2 tablespoons CMC sprinkled on top. Leave it sit overnight then blend it up with a stick/immersion blender. Use this CMC solution as part of the glaze mixing water, how much depends on what the application is.

[ATauer]

49 minutes ago, Min said:

What works with CMC is 1 US gallon of very hot tap water with 1/4 teaspoon copper carb plus 2 tablespoons CMC sprinkled on top. Leave it sit overnight then blend it up with a stick/immersion blender. Use this CMC solution as part of the glaze mixing water, how much depends on what the application is.

This is a great way to do it, I have only heard of directly adding the cu carb to the glaze! Which is still good to know how to do in case you forgot to mix up your glaze this way. For me I’m a little unsure how much I should use when mixing glazes, I spray versus paint (not brushing, but literally doing as they say “in a painterly fashion”) about 50:50. And while there are some glazes I will know I will definitely not be painting with (floating blues for example) a lot of glazes can go either way. What would you suggest Min? They are such different things, and when I paint a lot of time I’m diluting the glazes a lot to make them more like watercolors, or doing the opposite, thickening them with gum arabic to mimic oils or acrylics. And even if I don’t have a ton of glaze issues to worry about, I like having CMC in my glazes, it comforts me knowing the CMC is really attaching that glaze to the clay, even if it might dry a little slower, so what, I’m a sculptor, I’m not on a deadline to glaze 50 mugs in a day. 

Another thing I’d love some advice on is I’m going to be working soon on trying to optimize single firing my very large scale sculptures that are cut into sections to fit in the kilns, doing so would save me a bunch of firings. It is hard enough to figure out how to optimize it without spending the large amount of time to make a bunch of 6 ft tall sculptures to practice the firing and glazes on, thinking about how I might use this with single firing and likely with pretty long schedules because of the size of the pieces…although I don’t know that for sure yet, I make them out of paperclay porcelain, so their walls are actually quite thin even if they are huge. So they shouldn’t need as long as a regular large scale sculptor who use thick groggy clay with 2.5 inch-3 inch walls would…Would you recommend using this at all with single firing (which probably could benefit from it as the clay is not going to be as thirsty and porous as bisque), does it matter at all if it’s put on before bisque or if the glazes are fired for longer than is typical? Probably tough questions…

[Beebop]

4 hours ago, Min said:

If you do use either Magma or CMC be sure to add a tiny amount of copper carb to act as a preservative, it will work with either.

Do you think copper oxide be substituted for this purpose?

[Min]

3 hours ago, Beebop said:

Do you think copper oxide be substituted for this purpose?

No I wouldn't, could very well land up with speckles as copper ox. If speckles aren't an issue for you then reduce the amount by about a 1/3 as copper ox doesn't contain the CO2 that the carb does. Actually that would be 1/3 by weight.

[Min]

3 hours ago, ATauer said:

What would you suggest Min? They are such different things, and when I paint a lot of time I’m diluting the glazes a lot to make them more like watercolors, or doing the opposite, thickening them with gum arabic to mimic oils or acrylics.

Not sure on your question, are you asking how much CMC liquid to use in a dipping glaze that you will be brushing?

 

3 hours ago, ATauer said:

using this at all with single firing (which probably could benefit from it as the clay is not going to be as thirsty and porous as bisque), does it matter at all if it’s put on before bisque or if the glazes are fired for longer than is typical?

If your clay can take raw glazing I don't think adding CMC liquid should make any difference in the firing.

[ATauer]

2 hours ago, Beebop said:

Do you think copper oxide be substituted for this purpose?

I’ve only ever seen copper carb used for antimicrobial properties. I am not sure if there is any true difference in how it works, or whether there are different concerns for toxicity, I looked at an MSDS sheet for black copper oxide and compared it to copper carbonate’s, and there seems to be a bit more concern with copper oxide with inhalation and ingestion toxicity and its severity than with copper carb, ingestion we are going to rule out here as a concern so it is the MSDS sheet’s warning that inhalation could exacerbate other ongoing lung disease or from chronic exposure to cu oxide develop respiratory disease. It says the OSHA daily occupational limit is 1 mg/m^3 TWA, which with the small amounts we deal with and put in our glazes and especially in this CMC recipe I think it would be hard to get that high of a level of copper oxide in the air, even with dust and fumes, which is says to avoid of course. OSHA doesn’t even recommend wearing ventilators or dust masks unless the air levels are significantly higher than their limit, for up to their limit they just recommend good ventilation. 

So to try to come to a conclusion, I would suspect cu oxide would work just fine but can’t say 100% without testing because I just have seen it used for antimicrobial growth suppression. Copper carbonate is copper oxide with some added water, so honestly it is surprising to me they even have different MSDS sheets, but apparently they do have some slightly different issues with toxicity. I think there is no harm in trying and if your CMC enriched test glaze doesn’t go bad, then I would say go ahead and use it. It is too small of an amount to flux or color the glaze so there is little harm in it as long as you don’t eat it!

[ATauer]

On 7/30/2022 at 7:45 PM, Min said:

Not sure on your question, are you asking how much CMC liquid to use in a dipping glaze that you will be brushing?

 

If your clay can take raw glazing I don't think adding CMC liquid should make any difference in the firing.

They are not dipping glazes, they are sprayed or painted, and it isn’t brushing as I pointed out (which typically just involves quickly brushing the glaze with a hake in three coats letting it dry between and that is it), it is painting, which involves diluting or the opposite, making thicker with gum arabic usually and adding CMC and often polypropylene to help with the painting,-which involves applying with a variety of different kinds of brushes in varying thicknesses and amounts, usually not counting coats but going for certain affects, shading, doing it just like you would paint a watercolor or oil painting on a canvas.

So I’m asking how much CMC liquid the way you suggested making it up with the copper already in it as part of the water used for making the glaze. Right now, as I believe I said, I only add CMC to a separated portion of the main glaze for when I’m going to be painting. There are occasional times I also add it to a portion of a glaze that is going to be sprayed, if I feel for some reason it needssome extra help sticking to the bisque. Since they are NOT being dipped, ever, would you recommend altering your instructions, and could you give an approximate amount of CMC water to use when mixing the glazes. 

[Min]

17 minutes ago, ATauer said:

So I’m asking how much CMC liquid the way you suggested making it up with the copper already in it as part of the water used for making the glaze.

Replacing 1/4 - 1/3 of the water with the CMC liquid should get you in the ballpark. 

[ATauer]

3 hours ago, Min said:

Replacing 1/4 - 1/3 of the water with the CMC liquid should get you in the ballpark. 

Thank you! I have emailed Tony Hansen, who is such a wonderful human being about answering questions related to his blog posts, about his recommendation to have thixotropic glazes because of  much it improves dipping and a long list of benefits, about whether he would recommend doing it for spraying and painting the way I’ve described, since I have a spray gun that can handle super super thick glazes and even latex paint, but still works for delicate little ceramics pieces, so depending on his answer, I may be making my glazes significantly thicker and using Epsom salts with all of them. If I do that, since I’d be using less water, I will do some tests to see if I need to adjust the amount of CMC water (and try to remember to come back here and report on results) in a thixotropic glaze or not. Depends I imagine on just how much less water I would use.