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Brushing On Glaze?


PottaFella

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I've always dipped my pots, now I'm testing glazes in my own small kiln so I'm mixing quite small amounts of glaze to glaze smallish pots and need to brush or pour it on. Is it best to thin the glaze down with some water, because it seems to be going on very roughly compared with dipping? The bisque soaks it up so quick I don't have time to brush it out at all. Or should I maybe dampen the bisque first? Any tips, guys?

 

 

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Are these stoneware or earthenware glazes?  I find earthenware glazes relatively easy to brush, but stoneware are always a nightmare.  I've tried adding bentonite, wallpaper paste, and some liquid which I think is CMC, thinning the glaze, damping the bisque. I describe it as trying to brush icing sugar onto blotting paper.  I'm waiting for my class tutor to bring in some sodium dispex, hoping this might improve the brushability.  Having said they are a nightmare, if you can get good coverage, many of them do level out in the firing, and I get some good results. 

 

Try reading the Alfred documents that Norm posted, they might help.  Good luck.

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Thanks Chilly, yes it is stoneware glazes.

 

 

 

Are these stoneware or earthenware glazes?  I find earthenware glazes relatively easy to brush, but stoneware are always a nightmare.  I've tried adding bentonite, wallpaper paste, and some liquid which I think is CMC, thinning the glaze, damping the bisque. I describe it as trying to brush icing sugar onto blotting paper.  I'm waiting for my class tutor to bring in some sodium dispex, hoping this might improve the brushability.  Having said they are a nightmare, if you can get good coverage, many of them do level out in the firing, and I get some good results. 

 

Try reading the Alfred documents that Norm posted, they might help.  Good luck.

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I often brush my own stoneware glazes on (although spraying is beginning to take over), I make a solution of CMC (5mg to 1 pint of water)and add enough of that to thicken the glaze.

 

It won't need much, 20ml of the CMC solution to 100ml of glaze would almost certainly be too much:  it's going to depend on how wet they are to start with, but if I'm mixing small quantities of glaze I normally use 90 -100 ml of water to 100g of the dry glaze.

 

Then brush on three coats, the CMC stops the water from being instantly sucked out, but do remember you're not house painting, you're applying glaze with a brush, a soft fan brush is best.

 

(I would fret however, if my tests were applied in a different way to how I intend to make the finished product).

 

 

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I have been dipping, and pouring glazes for most of my life. I taught the kids that one glazed coat is equal to 3 brushed coats. At the same time I made certain to tell them to wash the pot thoroughly with a damp sponge before glazing to 1)remove any dust, 2) to have a little moisture in the clay to aid in the brushing. Not to dip pot in water, but to wash with damp sponge.  I usually mixed our glazes to a good dipping thickness where best coat was with two dips. This would allow color variations much more often. I also added Epsom salts and some bentonite if the glazed itself settled too much. Most of our formulas had sufficient clay to not cake hard.

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Adding bentonite allows more water to exist in the suspended glaze.  If you add enough bentonite, by the time the bisque is very wet and saturated with water the amount of glaze applied is still very little with a very, very thin layer.

 

Sodium Silicate or Sodium Dispex (Darvan in the US) will undo the changes created by bentonite and more, settling the glaze out allowing you to pour off excess water.  This is what you want to do if you are applying glaze to vitrified, previously glazed and fired, ware.  This way the glaze will apply like a syrupy slip and dry in place without running off the piece - per-heating the previously glazed ware to 200 F also helps.

 

Glazes without enough kaolin, clay, or bentonite, or brushing media like CMC or glycerin will dry in a thick layer the instant they are brushed on.

 

You want a balance.

 

Are these stoneware or earthenware glazes?  I find earthenware glazes relatively easy to brush, but stoneware are always a nightmare.  I've tried adding bentonite, wallpaper paste, and some liquid which I think is CMC, thinning the glaze, damping the bisque. I describe it as trying to brush icing sugar onto blotting paper.  I'm waiting for my class tutor to bring in some sodium dispex, hoping this might improve the brushability.  Having said they are a nightmare, if you can get good coverage, many of them do level out in the firing, and I get some good results. 

 

Try reading the Alfred documents that Norm posted, they might help.  Good luck.

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Ayjay, I make a solution of CMC (5mg to 1 pint of water)

 

Can you confirm the concentration? Regards, Peter

 

That's what I use (unless I wrote it wrong on the bottle). It's probably not critical, but for me it makes a fairly runny liquid, not so gloopy it won't mix in easily and thick enough that it works for me. You could almost certainly use a higher concentration if you wanted to.

 

The Digitalfire website suggests 30-40g of CMC per litre of water

 

I used hot water and a balloon whisk to make the original mix, (and added a teaspoon of disinfectant to stop it from honking).

 

Edit: I thought I'd corrected this a long time ago (may have been on another topic) but it's 5 grams - not 5 mg.

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I find Xanthan Gum from the baking aisle in the grocery a lot easier to use than CMC.  It mixes easily with cold water and has more powerful gelling ability.

 

As with CMC, Xanthan Gum, requires a disinfectant or bleach to prevent bacterial growth.

 

Xanthan gum, the outer cell wall of the Xanthanmonius bacteria, or something like that, is a newer and better technology than CMC.

 

 

Ayjay, I make a solution of CMC (5mg to 1 pint of water)

 

Can you confirm the concentration? Regards, Peter

 

That's what I use (unless I wrote it wrong on the bottle). It's probably not critical, but for me it makes a fairly runny liquid, not so gloopy it won't mix in easily and thick enough that it works for me. You could almost certainly use a higher concentration if you wanted to.

 

The Digitalfire website suggests 30-40g of CMC per litre of water

 

I used hot water and a balloon whisk to make the original mix, (and added a teaspoon of disinfectant to stop it from honking).

 

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Make a gum solution of 2 tablespoons CMC gum to 1 gallon of warm water. Also add 1/4 teaspoon copper carbonate as a preservative. It's not enough to affect the color of the glaze. Add the gum and copper to the water and let it sit overnight, then blend it up really well with a stick blender. Use this solution for 1/3 of the water when making your glaze tests. I have not found bleach to work well as a preservative. Personally, I like this mix better than Xantham gum. Try the mboth and see what you like best.

 

When I worked as a tech for a clay supplier, we used a mix of CMC and Vee-Gum T for our brushing formulas. Vee-Gum T is kind of pricey, so for testing your glazes it's not really necessary.

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  • 7 months later...

 

As with CMC, Xanthan Gum, requires a disinfectant or bleach to prevent bacterial growth.

 

Norm - I think I contaminated a bucket of transparent glaze by pouring back a small quantity to which I had added glycerin in order to brush it on. At least, I'm assuming that's what caused mould growth on the surface! I've strained off the lumpy bits and re-mixed, but suspect it's still contaminated. Re your quote above - can I add household bleach to the bucket to prevent further growth, without otherwise affecting the glaze? How much would I add to the remaining 2 1/2 gallons?

Thanks in anticipation.

Celia

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