gum in glazes

[Autumn Downey]

When I first started making glazes, gum was always added and I never questioned it believing it helped the application.  Recently I see information that suggests it might contribute to slow drying.  So, I am wondering if people who make their own glazes still use gum, what kind and with what results.  I believe we always used CMC at our Guild.  Lately, when I buy liquid gum, it has been gum arabic.  I'm not sure how I feel about it.  When I added a bit to an engobe it seemed to cause crawling of the glaze that the piece was dipped in.

Thanks for any information, thoughts.  

[Norm Stuart]

Gum burns out while Bentonite and Clay do not.

So the one glaze I add gum to is a "red cadmium frit "which is degraded to dark red or black with the addition of any bentonite or kaolin.

So I need the gum to suspend the frit and harden the glaze or frit and keep it attached to the bisque when it dries. Bentonite or 10% kaolin or clay in most glaze recipes can do this as well and better than gums.

Most gums are long strands of carbohydrates which attach to water and create a jelly-like suspension. They are a mild deflocculant (causing glazes to settle) and their addition makes the glaze take longer to dry. Guar gum is used in puddings and gravy (or glaze).  Guar gum and sand is used in fracturing oil wells because the addition of a little acid makes the guar gum suspension go as runny as water, locking the sand in place in the cracks as the watery guar gum drains away.

Gums without a preservative quickly turn black with mold. By adding 1% Sodium Bezoate and 0.5% dry Citric Acid the gum will not mold, and the citric acid is a flocculant which will counteract the deflocculating properties of the gum. All prepared liquid gums all have some type of preservative.

I add these preservatives to hot water and 10% by weight of dry gum arabic to make glass glue, to hold glass pieces together prior to doing a "Bullseye warm glass" firing.

I sometimes add to a ceramic glaze a "brushing media" like propylene glycol to help smooth out the brush strokes. In my experience Gums make a fairly lousy brushing media as you've noted.

Propylene glycol or glycerine do evaporate, but more slowly than water. Someone once suggested Floetrol paint additive as a brushing media, but I found it less useful than propylene glycol and more costly.

So I mix red iron oxide with propylene glycol to make "ink" to mark test tiles. If I add water, the ink pot is dried up by the following day. The propylene glycol takes a month to evaporate to dry red iron oxide, But it "dries" sufficiently on the test tile as soon as I write with it.

[Autumn Downey]

Thank you, Norm.  As a bonus, you have also given me the best explanation of fracking that I've seen, as it occurs in this area.

I do know that people make a lot of use of bentonite in glazes and pretty much every time I've tried it, I wished I had not.  That in particular seems to prevent the glaze from drying.  I do add Epsom's salts which sometimes helps (a bit but often not enough to make a real happy glaze application).   

I've been looking at some glazes to try but there are many that have little or no clay and call for bentonite.  Perhaps I will try, but very carefully!!  It is good to know about the propylene glycol.  I do have some in my engobe mix, but perhaps that's the ingredient that could be boosted up a bit in order to prevent crawling which has been more of a problem lately.  All my engobes are rather old so maybe that part of the mix has evaporated, as you suggest.

I also have some cranky glazes that dry and crack and tend to flake off if double dipped.  They are, I think also ones that lack clay.   One has bone ash and I just brought it up from the basement after about 15 years.  It hasn't improved!  But maybe I'll find a way around it.  Thank you for your help.

[Norm Stuart]

Bentonite, clay, calcium chloride and epsom salts all flocculate, making a glaze thicker. So people often add more water to thin it back down to their desired  consistency. A higher percentage of water obviously means a longer drying time. So in that way they're like gum, but for a different reason.

My perception is glazes which crack as they dry and peel off usually have soda ash, pearl ash, or nepheline syenite which contributed a lot of sodium or potassium ions which defloculate. Which might suggest adding more epsom salts or calcium chloride might help. I'll try that tomorrow.

"Crawl glazes" with a high percentage of magnesium carbonate also don't adhere well - and also tend to flake-off more in the kiln unless gravity is on your sides - ie being applied to the top of ware rather than the side of a piece. This is all the more noticeable when applied over a different glaze, because the first glaze remains well adhered while the magnesium carbonate crawl over-glaze flakes off.

I wish I could say betonite fixes those problem glazes, but if anything I seems to make it he flake-off worse. Quite annoying.

If anyone knows how to fix this problem with glazes which flake-off I'd appreciate knowing how.

Autumn Downey said:

Thank you, Norm.  As a bonus, you have also given me the best explanation of fracking that I've seen, as it occurs in this area.

I do know that people make a lot of use of bentonite in glazes and pretty much every time I've tried it, I wished I had not.  That in particular seems to prevent the glaze from drying.  I do add Epsom's salts which sometimes helps (a bit but often not enough to make a real happy glaze application).   

I've been looking at some glazes to try but there are many that have little or no clay and call for bentonite.  Perhaps I will try, but very carefully!!  It is good to know about the propylene glycol.  I do have some in my engobe mix, but perhaps that's the ingredient that could be boosted up a bit in order to prevent crawling which has been more of a problem lately.  All my engobes are rather old so maybe that part of the mix has evaporated, as you suggest.

I also have some cranky glazes that dry and crack and tend to flake off if double dipped.  They are, I think also ones that lack clay.   One has bone ash and I just brought it up from the basement after about 15 years.  It hasn't improved!  But maybe I'll find a way around it.  Thank you for your help.

[Autumn Downey]

Thanks again.  I just made a test glaze today which had almost everything that could be difficult in it, but the good feature was a about 7% kaolin and 3% Gerstley borate, and it seemed to apply quite well.  I think I will watch for these in any future glazes.  Of course, it still needs to be fired, but this part at least was satisfying!    I have also decided that in overlaps, the good glaze needs to be over top of the difficult glaze which improves the chance that it will stay on.   I think you said as much.  

I've saved most of my not-so-good glazes, which in general do have enough silica.  Eventually, I will probably try to combine them into a mystery glaze - hopefully something wonderful even if  impossible to reproduce.

[Autumn Downey]

Hello Norm,  I was thinking to get some propylene glycol or glycerine. Probably a pharmacy or health food store for glycerine, I suppose.  I have a little of each left from purchasing a long time ago, and think the yellow prop gly was just a non toxic antifreeze.  It seems to work fine but is almost gone.  When I look now, all the non-toxic antifreeze seems to be combustible and probably is mixed with something else.  I had imagined this would not be difficult, but it doesn't seem quite straightforward either.    Thanks, am sure I can find glycerine in any event.    

[Norm Stuart]

The glycerin is more of a humectant which attracts moisture.

For chemicals I use Amazon or Ebay.Much cheaper and in better containers than a ceramics supply place likeLaguna.

https://smile.amazon.com/gp/product/B006TTQTH4/ref=oh_aui_search_de...

Buy Propylene Glycol not Ethylene Glycol which is a poison if eaten.

Even stuff like Sodium Silicate. I like the containers with handles. https://www.ebay.com/itm/Sodium-Silicate-37-5-Type-N-1-Quart-Water-...

Or Calcium Chloride https://smile.amazon.com/gp/product/B005Y34T3W/ref=oh_aui_search_de...

[ravi chandran]

How much propylene glycol to be added to dry glaze mix any reference points thank you

Norm Stuart said:

Gum burns out while Bentonite and Clay do not.

So the one glaze I add gum to is a "red cadmium frit "which is degraded to dark red or black with the addition of any bentonite or kaolin.

So I need the gum to suspend the frit and harden the glaze or frit and keep it attached to the bisque when it dries. Bentonite or 10% kaolin or clay in most glaze recipes can do this as well and better than gums.

Most gums are long strands of carbohydrates which attach to water and create a jelly-like suspension. They are a mild deflocculant (causing glazes to settle) and their addition makes the glaze take longer to dry. Guar gum is used in puddings and gravy (or glaze).  Guar gum and sand is used in fracturing oil wells because the addition of a little acid makes the guar gum suspension go as runny as water, locking the sand in place in the cracks as the watery guar gum drains away.

Gums without a preservative quickly turn black with mold. By adding 1% Sodium Bezoate and 0.5% dry Citric Acid the gum will not mold, and the citric acid is a flocculant which will counteract the deflocculating properties of the gum. All prepared liquid gums all have some type of preservative.

I add these preservatives to hot water and 10% by weight of dry gum arabic to make glass glue, to hold glass pieces together prior to doing a "Bullseye warm glass" firing.

I sometimes add to a ceramic glaze a "brushing media" like propylene glycol to help smooth out the brush strokes. In my experience Gums make a fairly lousy brushing media as you've noted.

Propylene glycol or glycerine do evaporate, but more slowly than water. Someone once suggested Floetrol paint additive as a brushing media, but I found it less useful than propylene glycol and more costly.

So I mix red iron oxide with propylene glycol to make "ink" to mark test tiles. If I add water, the ink pot is dried up by the following day. The propylene glycol takes a month to evaporate to dry red iron oxide, But it "dries" sufficiently on the test tile as soon as I write with it.

[Norm Stuart]

Add a brushing media like propylene glycol (a liquid) to glaze after you've already added water and sieved the glaze.

Just one percent or so improves the flow in chalky glazes when applying. Propylene glycol does evaporate, but slower than water.