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fruch

Dipping Bisque into Clear Glaze

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Hello Everyone:

I am having some problems with some clear glaze. I purchased a 5 gallon bucket of Amaco low firing clear glaze for dipping. I did my first test fire on two plates. The results were very undesirable. When I dipped the plates and pulled them back out of the glaze there were a lot of bubbles on the surface of the plate. The bubbles did pop on their own and  those that didn't I popped myself.  I was a little concerned but figured I would fire them anyway and see what happens. Just as I suspected the glaze separated in certain areas around the plate. I did  another two plates and got the same results. I am not sure what is happening. I am mixing the glaze with a drill and mixer. I have done this with other glazes and have not had a problem. Do I need to mix the glaze and wait a minute or two before dipping? I am glazing on a low fire bisque so that should not be the problem. 

 

 

 

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Thanks for the help. I always wash my bisque before glazing. I do all my glazing in one session so I don't think any dust would get on the pieces in that short amount of time, I also use a turn table when glazing to avoid finger prints and when I dip I use tongs. I thought of all those things that is why I am a little stumped. I want to use this glaze with my students so I need to get this figured out. We have a small budget  so I don't want to waste this glaze. Any additional thoughts or ideas. 

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Glaze crawling can be caused by a lot of factors.  In addition to what Bruce has mentioned, I would look into glaze thickness, whether it's flocculated, and drying times.

The bubbles suggest to me the glaze was maybe applied too thick?

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Since your other glazes are not crawling my guess would be too thick a layer of glaze like Tyler said. I would measure the specific gravity of the glazes that don’t crawl and compare those figures with the sg of this clear. Does Amaco give a sg for this glaze? Are they in the bucket for too long? Are these the only pieces you dip and are they thin slipcase pieces? When you do the next tests I would scratch thru the dried glaze to see the thickness of it on one piece, then fire the other piece(s) and keep the unfired piece for reference of glaze thickness. 

Re bubbles, are there bubbles in the glaze slurry after you mix it up? If that’s the case then I think stirring rather than the mixer might be better. If there is a bubbly froth on top of the glaze a few spritzes of hairspray or alcohol into the slurry will pop them. If there isn't froth or bubbles on the surface of the glaze slurry then it sounds like you just need to give them a good rub with your finger as they would be from minuscule air pockets escaping through the drying glaze. Did you smooth out the popped bubbles with your finger prior to firing? I’m assuming the bubbled areas are not the areas with crawling like in your picture? Is your bisque fire hotter than your glaze fire?

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I am firing the bisque at ^04 and the glaze at ^05.  I have always fired at this temp but usually brush the clear on. I was trying to find a faster way to clear coat so I thought dipping would be a good solution. I did not rub the bubbles out. I thought perhaps the glaze would melt enough and fill them in. There are bubbles on the surface of the glaze after I have mixed it whether it is hand mixed or with an electric mixer. I will spray it with some alcohol and see what happens.   I have a two more plates I am going to fire. I mixed the clear and tapped the bucket to settle the bubbles before dipping. But, I still got air bubbles on the plates. I'm still at a loss. 

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Trying a lower bisque temperature than your glaze might help, it also looks too thick to me.  The thinner I can put clear glaze on the better.   I don't use a drill mixer unless the the bucket is old and settled.  I use a 5 gal wood  paint paddle that you can get at a paint store.   Denice

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I still think you have 2 things going on. 1 is the bubbles and 2 is the crawling. 

Bubbles are not a big deal if you rub them over when the glaze is dry. You can spritz alcohol or hairspray into the glaze slurry before dipping if there are a lot of them in the bucket.

The bare spots where the glaze has pulled back looks like crawling to me. My guess for why you are having it is putting on the glaze too thickly. Either the glaze is mixed with too little water or the plates are building up too thick a layer by being in the bucket too long. This is why I suggested measuring the specific gravity of the glaze. Like Denice said clear glazes can often go on quite thinly. I always try test tiles with 1, 2 and 3 thickness of glaze. How did you determine how much water to add to the dipping glaze and / or adjust it?

Edited by Min
typo

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The crawling has nothing to do with the bubbles. The issue could be thickness, since brushing glazes are usually mixed thicker than dipping glazes, or possibly too much water. When glazes are mixed for brushing they add a gum solution that allows the glaze to hold more water. This allows them to brush more smoothly and dry slower. So if you're washing your bisque and then dipping a brushing formula you're totally saturating your pots, which loosens the physical bond between the clay and glaze before it melts. Then once it melts it pulls away and crawls. I do a lot of double and triple dipping on my pots, and if I don't let things dry enough between dips they get over saturated and the glaze crawls. You don't want to let them dry completely between dips, but enough that the pot can take in the water of the next dip without becoming overly wet.

So, you either need to let your pots dry completely after washing them so you're starting from zero water content in the pots, or you need to use glazes that are made for dipping, not brushing.

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I'll re-post a pic of the plates that are firing right now in a day or two. Thanks for all the suggestions. If these don't turn out I may go back to brushing the clear on. The clear I am dipping in is for dipping not brushing.  Is it alright to brush on dipping glaze or will it fire badly? 

Edited by fruch

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17 hours ago, fruch said:

Thanks for the help. I always wash my bisque before glazing. 

 

1 hour ago, fruch said:

ok, good to know. I am not washing them before I dip because I have underglaze on them.  Maybe I should thin the glaze with water? 

So you wash them unless they have underglaze?

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If you're not thinning glaze you normally would brush on then you're applying glaze too thickly.

testing would help you get the required thickness.

Are your glaze buckets big enough to dip entire piece, or are you overlapping glaze on some area of your work?

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I use a clear that I have mixed.  I have never achieved the desired result with brushing or dipping.  I spray.  That gives me a nice even, consistent application.  But my clear has to be thin.  To Spray, to brush, to dip.  I really think your clear must have been too thick.  I was taught to hold a bisque piece under a running faucet and scrub it before glazing.  I did not like the results.  I switched to a damp sponge wiping down the piece.  Then I put the underglaze on.  That works better for me.

Roberta

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Couple things. I do wash right under the tap so I'll switch to wiping with a sponge before glazing period. Second, I thinned the clear glaze with water and that solved the problem. I was a little hesitant because I didn't want to make it to thin. But, it all worked out and it seems to be firing properly now. I do not have a viscosity scoop, is there another way to check this or does anyone know approximately how much water should be added to a 5 gallon bucket of amaco clear glaze for future thinning?  Thanks for all the advice. I learned a lot. 

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46 minutes ago, fruch said:

Couple things. I do wash right under the tap so I'll switch to wiping with a sponge before glazing period. Second, I thinned the clear glaze with water and that solved the problem. I was a little hesitant because I didn't want to make it to thin. But, it all worked out and it seems to be firing properly now. I do not have a viscosity scoop, is there another way to check this or does anyone know approximately how much water should be added to a 5 gallon bucket of amaco clear glaze for future thinning?  Thanks for all the advice. I learned a lot. 

Take a scale and a beaker that has 100ml on it. Fill the beaker up to 100ml and look at the weight. That amount divided by 100 is specific gravity.

For example: put a beaker on a scale and zero it out. Then you fill the beaker up to 100ml and look down at your scale and it says 154g. Then you know the specific gravity of that mix is 1.54 (154/100). So next time you make that batch up. You can add water and get it close, then measure and adjust until you achieve the same goal. 

This is the quick and easy way. 

Glad your glaze is working now. 

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Thank you. I added another pic. I think all the glazes I am using are simply to thick.  I applied Mayco Stroke and Coat SC 87 to a bowl. The jar says 2-3 layers for opaque color. This is what I did and still got chipping. I fired at ^05. Does the chipping have to do with applying to thick. Apparently this is my achilles heel. 

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It could be a number of things.  It is difficult to tell by a single picture. To me it looks like that was scraped while it was being loaded or stuck to another pot when fired. Just by the way it is shaped. I don't know much about brushing, so I can't comment. But in general thick glazes are difficult to work with unless you formulate them to go on thicker, by calcining them before adding them to a glaze mixture.  If your using commercial glazes this will be impossible. If I was using commercial glazes I would want to apply them as thin as I could without losing the quality of the glaze that your after. This would save you both time and money(over use of glaze).

The best way to figure this stuff out is to test. Make some test tiles or small test cups and brush the same way you do now, but do 1 coat, 2 coats, 3 coats, ... n coats. Write down everything and just look and see. You could achieve the same color with 1 coat as 2. Thus saving you massive amounts of work and glaze. But you would have to be adamant to work the same way you do now. 

Good luck!

 

Edited by Joseph F
spelling and grammar

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I see what you mean by the way it looks. I didn't hit it against anything though. I usually do test tiles and this one in particular turned out fine. Unfortunately, when I actually put it on a bowl I didn't have the same luck. Thanks for all the advice. I will make a few more test tiles and keep working at it. 

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10 hours ago, fruch said:

I see what you mean by the way it looks. I didn't hit it against anything though. I usually do test tiles and this one in particular turned out fine. Unfortunately, when I actually put it on a bowl I didn't have the same luck. Thanks for all the advice. I will make a few more test tiles and keep working at it. 

@fruch

I didn't mean to say that you did. If I came across that way I am sorry. I just know that I have bumped pots before and I looked at it and the glaze was still in tact. However when I later fired it the glaze crawled in that spot where I bumped it. Sometimes when you have a thick layer of glaze it can crack under the surface from stuff as simple as a bump, then you don't notice it unless you look really close and after you fire it. Boom. It pops off during the firing or crawls etc. 

Either way let us know how it goes!

Edited by Joseph F

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On 9/29/2017 at 6:17 AM, Joseph F said:

@fruch

I didn't mean to say that you did. If I came across that way I am sorry. I just know that I have bumped pots before and I looked at it and the glaze was still in tact. However when I later fired it the glaze crawled in that spot where I bumped it. Sometimes when you have a thick layer of glaze it can crack under the surface from stuff as simple as a bump, then you don't notice it unless you look really close and after you fire it. Boom. It pops off during the firing or crawls etc. 

Either way let us know how it goes!

O' No worries. I didn't take it like that. I was just responding. I appreciate all the suggestions and help

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