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clayshapes

single firing, cone 6 stoneware

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try the search part of this website.  this topic has been discussed often.  it is not rocket science but there appears to be a LOT of confusion regarding this practice.  i do not want to type out lots of info that nobody will read so i recommend using the search method since nobody will look at a book anymore.    the internet has many, many errors due to the fact that anyone can enter anything, it ain't all GOOD information.

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9 hours ago, RonSa said:

Also, it seems the glazes needs to be applied thicker when single firing.

Do you think so? A potter I was assisting was spraying her glazes on greenware it was pretty thing but we never had any issues. Did you run into any troubles?

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Use the same glazes you have always used. If spraying glazes onto greenware look for, thank you OldLady, a "chunky velvet" surface to know when enough glaze has been applied.

Change your glaze firing schedule to incorporate these 2 segments at the start of the schedule. Or not. This was taken from Steven Hill.

Segment        Rate F*/HR    Temp    Hold
   1                        200                   220     30-60

   2                        100                   500      0
5a0a1bb97cc06_chunkyvelvet.JPG.5fd8104bd8c1d5670d7e96328cfb4656.JPG

This is chunky velvet. Notice the glaze cracking. The glaze is a tiny bit too thick in that spot. 

Below is after the glaze firing...

5a0a1c229908e_bluesoupmug.JPG.f1e65283d90f84809cea6996860e6da5.JPG

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51 minutes ago, Judith B said:

Do you think so? A potter I was assisting was spraying her glazes on greenware it was pretty thing but we never had any issues. Did you run into any troubles?

Yes I did.

On 8/13/2017 at 1:27 PM, Tyler Miller said:

It ends up going on thinner with greenware if dipping. The water absorption is less than bisque. Especially since its best to dip greenware when just a little water is left.

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think get better results with a certain percentage of clay in glaze, from memory, 20% but test.

a thicker glaze soln. is advised because the porosity of non fired clay greater than bisque , thicker less water therefore adequate glaze deposited on pot with less shrinkage is my logic today

Edited by Babs

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thank you, john for the clear photo showing chunky velvet and the smooth part that tells me it is too thick.  excellent photo and great explanation.  i use any glaze, never worry about what is in it just the application.  so much odd superstitious belief about such a simple thing.

it is true that i am self taught and maybe i have just been successful at single firing by accident.  someone recently said some of us have been walking on the edge of a cliff and maybe that is me but "try it and see"  seems to work.

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I've been single firing for a quire a few years now and in my experience just about any glaze will work but the main issue you run into is having the glaze stay put. Some glazes with Gerstley Borate will gel on their own and apply evenly and stick to the pot. Others require Gum Arabic to stay on or they flake off and this always leads to crawling. What works for me and glazes that wont apply nicely is 4 grams of Gum and 80 grams of water per 100 grams of dry ingredient. This will require about 3-4 coats but you can cut the water in half and apply in 2 coats, cut it again and apply 1 coat. Depends on how thick you can get your glaze before its unbrushable.

Some recommend leather hard glazing but I find bone dry because if you glaze on leather hard the clay continues to shrink but the glaze doesn't (it flakes and falls off).

You can also pour the insides at bone dry just dry it out slowly. 

Depending on how far you want to go you can also mix certain clays together as some react better to water absorbtion. My stoneware always cracks but adding in 1/6 of Terra Cotta helped it go through the shock of water and after firing the bonus of a stronger feeling clay body. 

It just takes a little patience and a little courage.

 

Edited by BlackDogPottery
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I've mostly single fire and can second a lot of what has been said.

Get Fran Tristram's book "Single Firing".

Your clay body and glaze both need to mature at the same temperature, and this is what you fire to.

You can brush, dip pour or spray but you may need to adjust the thickness and the time of application (leather hard, dry etc) - as with everything in pottery experiment and testing is the way forwards as what works for one person may not work in your situation. Many standard glazes will work as they are but some glazes will need adjusting if their drying shrinkage is different to the body shrinkage (glazes with moderately high clay content helps here), or adjust the timing of when you apply. I had one commercial glaze would flake off after drying when I applied it on leather hard so I applied it on dry and it was fine.

Some glazes will come out more or less the same while others will have altered colour or surface texture. You can get more interaction between the glaze and clay - what is it they say, something like "the glaze is the lens you look at the body through." Again, test and use what works for you. 

If you pour or dip dry ware you may have problems with the shock of new water absorption causing damage. Wall thickness needs to be even and avoid sharp corners, not too thick, not too thin. It can help to lightly spray one surface with water when applying glaze to the other surface. Sometimes when applying glaze to the second surface the absorbed water drives air ahead of it causing blisters on the first surface - changing your sequence or the timing between applications can help.

Firing schedule - basically you are combining the bisque and glaze firings in one so need to go slowly and good ventilation up to 800-900C to burn everything out, start with your normal bisque profile and at the end of that  you can ramp up to highest temp fairly fast.

Good luck!

Joe

Edited by Joe_L
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If you are spraying onto greenware, having your Specific Gravity between 1.50 and 1.60 will help the application. 

I pour glaze for closed forms, then let the pieces dry overnight before glazing the outsides. For bowls I will spray the outside first then flip it over and spray the inside. I have never had the greenware bloat from water or have glaze falling off. 

The biggest change, for me going to single fire, was remembering to handle the piece with dry hands. And the amount of glaze to apply to greenware - it takes more glaze.

Like OldLady I am walking close to the edge. Self taught. There was no easing in to single fire - I jumped in with both feet - never even thought about altering the glaze - all 28 of them.

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best tools for single firing are a stack of towels.  good old  terrycloth cotton from the dollar store or thrift shops.  your hands will go from wet to dry a billion times on glaze day.  dry is important.

john, i never thought it took more glaze to spray single fire, i save the overspray and use it as a glaze when i  have accumulated enough quantity, usually a 2 gallon bucket a year.

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I can't imagine doing it on a regular basis unless I strictly sprayed and even then probably wouldn't bother. I see bisque as the step to get the pots ready to work with.  Moving 50-60 pots around to get ready for and do a glaze run (often late at night pushing a load through) would just be too fussy if I was working with greenware and it would piss me off when I lost pieces and I am heavy handed enough that I would lose pieces all the time.  I just like working with sturdy bisque ware.

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On 11/17/2017 at 9:06 PM, oldlady said:

i save the overspray and use it as a glaze when i  have accumulated enough quantity, usually a 2 gallon bucket a year.

I tried that and while I wasn't up to 2 gallons it was more like 1 pint when I decided to dip a tile in the glaze and fired it. The results were an ugly brown. I'm up to a half gallon and counting.

I'm guessing my problem is  you may only use 1 or 2 glazes where as I mixed a potpourri of commercial and studio made glazes.

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Scrap glaze
At the college we have more than 10 glazes ranging from clear through the whole spectrum to black and white, along with a  barrel of 'wash water' where the stirrer is washed.  Any unused glaze from testing assignments or "whatever experiments" along with leftover glazes goes into a 10 gallon barrel labeled "scrap." 
Scrap is constantly changing.  It is used to glaze the insides of bottles and jugs.  It is often used as a background coat for applying contrasting texture, color, or 'value' (light-dark) glazes over it. 
Even after 5 years the scrap barrel has not overflowed.  We did have it go to almost empty a couple of  semesters ago.
Some students prefer scrap because it is always interesting
.
I always use the "wash water" to tint the "unglazed" areas on vases, bowls, sculpture, and foot rings.  
lt
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ronsa, yes, the color could be bland if you just take whatever comes and save it all.  i hope i use a little judgement when glazing and save those colors i know will come out somewhat useful with only a little addition of more stain or carbonates to tweak the color.  most of them are pale or my usual green and cobalt.  those are saved, the black and dark red brown are the final colors of the day and they are not saved.  

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8 hours ago, Magnolia Mud Research said:
Scrap glaze
At the college we have more than 10 glazes ranging from clear through the whole spectrum to black and white, along with a  barrel of 'wash water' where the stirrer is washed.  Any unused glaze from testing assignments or "whatever experiments" along with leftover glazes goes into a 10 gallon barrel labeled "scrap." 
Scrap is constantly changing.  It is used to glaze the insides of bottles and jugs.  It is often used as a background coat for applying contrasting texture, color, or 'value' (light-dark) glazes over it. 
Even after 5 years the scrap barrel has not overflowed.  We did have it go to almost empty a couple of  semesters ago.
Some students prefer scrap because it is always interesting
.
I always use the "wash water" to tint the "unglazed" areas on vases, bowls, sculpture, and foot rings.  
lt

I have one of those too that I throw all my unused white glazes and sometimes a little bit of slip. Interesting thing to see how some of the whites change to the creamier side or grey side with usually a few soft specks of cobalt and copper (from the clays I guess)

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I thought about adding some cobalt or copper to the glaze. Stain is an idea too.

Inside of closed forms (jugs and bottles) is a good way to use up scrap glaze

Thanks for the responses. 

 

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You can modify a scrap glaze pretty easy if you really want to.

Mix up the scrap glaze really well, then take out 100ml of it for a sample of the main batch. Add some amount of coloring to it, make sure you record everything. Say you add 2 grams of dry copper carb or something, dip a tile, add 2 grams more, dip a tile, add 2 grams more dip a tile. Fire these tiles, find the one you like best. Estimate the amount of glaze in the bucket. If its a 5 gallon bucket half full just do the math. For example a 5 gallon bucket half full is roughly 9500ml. If you liked the 4 gram addition. That would be 4%. So you multiple 4% times 9500 and get 380. Thus you need to add 380 grams of copper carb to your big batch to get roughly the same coloring. Of course you and continue to add more later on so it might be best to do like 250-300g and fire it to make sure then add more until you get it right.

You can also do this same thing if the scrap glaze is to runny or too stiff. Just add flux or clay in the same way.

 

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6 hours ago, Magnolia Mud Research said:

... an intriguing idea ...
it would require standing up, walking 25 meters from the throwing studio to the 'scrap barrel" in the glazing studio and returning without my hands drying or dripping. 
LT

or, you could think ahead:-\ and have a container beside your wheel at start of throwing.

up and walk and stretch is a good practice to fit into your work at wheel however.

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