Single Fire Cone 6 Oxidation

I have posted this in the single firing group and no one seems home so I'm reposting here.

I'm about to dive into single firing. The only issue I see is Oxidation has a rather flat and dull pallet in general. For color I'm currently using Pinnel's Green, Randy's Red, Honey, and Floating Blue. The only glaze I may be able to keep is Pinnell's. None of the other's have enough clay. I will be wanting to move away from using Gerstley in any case and will be working off of MC6 glazes that have high clay content. Is anyone else firing oxidation (and cone 6) and are you satisfied with your color palette and surface? Thanks, Donna

P.S. The Pinnell's did not work on leather hard. Flaked right off. I really did have fun glazing and then trimming though so I'm very excited about going this route. Palette is the only issue for me.

Reply to
DKat
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One piece of advice that may help you (it's helping me), was made by the late Andrew Holden, a British Potter who wrote on single fire in the '80s. This was that up to 3 percent Bentonite can help lower clay glazes convert.

Steve Bath UK

In article , DKat writes

Reply to
Steve Mills

Thanks Steve. Do you happen to know and to remember how to calculate the weight of ingredients in a glaze from specific gravity? Once upon a time (I'm talking decades here) I think I knew....

Reply to
DKat

I found this a little while ago, and as I'm mathematically challenged I kept it. I quote:

For the mathematically challenged, here's another way to find the weight of dry ingredients in a 1 litre volume of glaze. Let's agree to use the letters "SG" for the density of the glaze in grams per millilitre. I'm told it's politically incorrect to keep calling it "specific gravity", but it's the same thing.

Now the weight of dry matter in grams, in 1 litre of glaze, will be

1625(SG-1), assuming an average value of 2.6 grams per millilitre for the dry ingredients.

For example, if the SG of the glaze is 1.3, the dry matter in 1 litre will be 1625 (1.3-1) which is 1625 x 0.3 or about 487 grams.

Another example: If the SG of the glaze is 1.4, the dry matter in 1 litre will be 1625 x 0.4, or about 650 grams

That didn't hurt much, did it? Not witchcraft. Just Brongniart's formula rearranged. A lot simpler to calculate than when set out in the usual way.

John Rogers also wrote a piece on calculating glaze density and viscosity in Clayart on May 20th this year:

Hope this helps

Steve

In article , DKat writes

Reply to
Steve Mills

May I call you a doll? In any case it is much appreciated. Just what I needed (I want to play with my existing glazes rather than mixing up new batches). Thanks a lot!! Donna

Reply to
DKat

Ok, I've been doing a lot of playing around. Some glazes seem complete secure. Others seem fine except for on the lip. This has flaked off. Have you had this problem and is there any way to recover from it. I'm working with little tiny bowls right now so they are fairly tolerant. Do I spray the entire pot to dampen it and then just dip the lip? Do I paint the lip with corn syrup and then dip? Anyone have experience with this? I want to fire the pieces to see how the glazes look but as is they would then have to be thrown out.

Also are you glazing bone dry or leather hard?

Thanks, Donna

Reply to
DKat

Dear Donna,

By and large I'm glazing leather hard, but I'm having a problem with one glaze that's basically granite slurry and I'm forced at the moment to glaze onto Bisque.

Applied thickly it is amazing, but runs like blazes, and saturates dry unfired ware. If I try to add clay to it, it looses all its character. I've tried Bentonite, but no go, also I've added same Gum Arabic in an effort to get it to hold onto leather hard, but that doesn't really work either, so I'm between a rock and a hard place at the moment!!

Mark you, if it was all easy it would be boring wouldn't it :-)

Steve

In article , DKat writes

Reply to
Steve Mills

Granite will do that to you (put you between a rock and a hard place). What of spraying or brushing corn syrup on the bone dry piece and then pouring/dipping the glaze? I'm entirely making things up here but it seems the syrup might cut down the water absorbtion and get the slurry to stick.

How much bentonite changes the character of a glaze. I was about to just by default add 3% to the glazes I have but I don't want to do that if this is an issue.

Thanks, Donna

Reply to
DKat

I just read about heating up the pot before glazing. It says to heat it up as hot as you can handle. That cuts down on absorption and stress....

Reply to
DKat

In article , DKat writes

The latter could be worth a try. I'm avoiding spraying if possible.

more than 3 percent I think, but I've never gone over that. The effect on the Slurry glaze is to diminish the rich green Hare's Fur I get with the undiluted material, not by much though.

Take care

Steve

Reply to
Steve Mills

Regarding the last question, you have to be very careful when glazing bone-dry ware: If it absorbs too much water, the body can crack. Sometimes the cracking is not obvious until after firing. I have given up using pour and dip methods on bone-dry single-fire, but I suspect spraying would be OK since you could keep it dry. (I am avoiding spraying since I don't have a setup for that.)

Something else you might want to consider, at least for experimentation if not for production, is using a base other than water for pour and dip glazing of bone-dry ware. The idea is that water rehydrates the body and causes expansion cracking, but some other vehicle may not. So far I have only tried oil (canola). I just mixed up the regular glaze recipe but added oil instead of water. This basically works, but it is really hard to use because the glaze is left as a vrey loose powder on the surface of the piece... reminds me of butterfly wing scales. So I ended up with unavoidable finger smudges just from moving the ware into the kiln, etc. But for a production operation you might be able to use tongs or something.

I suspect any non-aqueous solvent would be a good candidate to try. The problem is finding one that is cheap and safe. For example, concentrated alcohol might work, but who can afford that except for someone-off masterpiece? And various low-weight solvents might work, but who wants to have gasoline or xylene, etc, in the studio?

If anyone has any ideas for other solvents, I'm all ears!

Best regards,

Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis

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Home of DaqGen, the FREEWARE signal generator

Reply to
Bob Masta

So do you have any idea what is in corn syrup? I assume water is the main component but I don't know. What would happen if you painted the piece with corn syrup when wet or leather hard and then glaze when bone dry.... Going to go try.

Reply to
DKat

I'm lucky over here; most of the clays I use will handle glazing while dry.

I've just realized an answer that's been staring me in the face;

We found out while being Ceramic Suppliers that turning a glaze into a brush-on almost without exception made it absolutely fine for raw glazing regardless of the ingredients. The addition of CMC seems to work the magic. It was a chance discovery by a customer accidentally glazing some kids earthenware models with commercial brush-on glazes without bisque firing them.

The most important thing to remember though is that CMC is an organic material, so MUST have some anti-bacterial material in it to stop it going *off*!

I have a copy of the original information sheet we used to hand out, so I have copied it and pasted it below.

Email me if you have any questions, remember to do what it says in my address at the top of this post.

Note: Glowkil is an odourless commercial anti-bacterial preparation which we used and sold. I can't supply any of this stuff now!

Steve Bath UK

BATH POTTERS' SUPPLIES Guidelines for making your own Brush-on Glazes

The process of making up your own brush-on glazes is fairly straightforward. However two important rules need to be observed:

1) make-up the glaze as for a standard dipping glaze. 2) when stirring in the CMC, use a medium or slow means of stirring; because fast stirring will make the organic polymer overheat and become stringy.

Basic recipe for earthenware glazes To make 2 gal:

6 kilos glaze base powder e.g. B276. 9 litres of water. 270 grams CMC (organic polymer). 120 grams Glowkil (an anti-bacterial solution that increases shelf life). Colour. Mix glaze, water, and colour together to the right proportions for dipping glaze. Slowly add CMC. Stir well, for at least one hour. Allow to stand for half an hour, add Glowkil and mix for a further ten minutes, and then bottle down. If you are going to leave the resulting glaze in the bucket, remember to stir well before using it.

Stoneware glazes

2 gal prepared glaze. 100 g CMC per gallon. 45 g Glowkil per gallon. Mixing instructions as for earthenware.

Raku brush-on glazes are very tricky to construct as the recipe varies with each different coloured glaze. So it is down to trial and error using the earthenware recipe as a starting point

Note

1) Glazes containing bone ash will need the amount of CMC in the recipe reduced, the proportion will vary according to the amount of bone ash used. Trial & error is the technique here as there are no hard and fast rules. 2) Glazes containing Calcium Chloride glaze suspender are not suitable for converting into brush-on glazes 3) These proportions are for UK based materials. Be prepared for variations in materials local to you!

In article , Bob Masta writes

Reply to
Steve Mills

Does it really mean stir for one hour? I won't even do that for carmels (made with thick cream, sugar and corn syrup - to die for - literally). Thank you again! Donna

Reply to
DKat

I'm afraid so, I have a paint stirrer I shall set up clamped to the bucket so that I don't get arm ache!!

Steve

In article , DKat writes

Reply to
Steve Mills

Corn syrup is so concentrated that the tiny amount of water in it is unlikely to be a problem... especially since you are only going to brush it. In fact, I have had decent success brushing on conventional water-based glazes just by using multiple thin coats and allowing adequate drying between coats. The cracking problems have only been with dipping and pouring.

Best regards,

Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis

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Home of DaqGen, the FREEWARE signal generator

Reply to
Bob Masta

So heres the deal - most of the glazes I tested worked just fine except for the lips where at least half of them simply flaked off. I hate to put these pots through any more stress so I'm going to try painting on the lips a very thin coat. Do I do this by thinning down the glaze or what? Do I add corn syrup to the glaze and if so in what ratio? Thanks, Donna

Reply to
DKat

Do you think an electric mixer set at very low speed (folding or breadmaking) would work?

I thought I was being very clever and put my bentonite in water before adding it to the glaze. I'm now de-lumping it by putting batches in my blender (we are not going to tell spouse and kids this). It makes are really wonderful goo!

Reply to
DKat

I've done some raw glazing and I took some notes on it from a book. Naturally, the notes aren't here. I think I remember that for flaking on the lip, you may need to reformulate the glaze. It may be a simple change i.e. instead of kaolin use ball clay as it's more elastic. If the recipe doesn't have kaolin...I'll try and pick up my notes.

The only time I tried syrup it was icky. But it was for a re-glazing and I may have used too much.

Elaine

Reply to
Elaine Stutt

Thank you. Every bit helps. I never have refired well. Other than being icky did the syrup work?

Donna

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Reply to
DKat

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