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Proper Glaze Procedure?


dhPotter

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Seems I remember reading to glaze the inside then let it dry overnite, then glaze the outside. If overlapping I have read to wait till the first layer is completely dry, not just till the sheen goes away, then added the overlap glaze.

 

In the pics the naked clay is where the glaze moved away from the body, after the glaze firing, both from a horizontal and vertical surface. Thinking it was finger oil/ grease, I have gone to handling bisque ware with gloves, from the time it is taken out of the kiln till it is placed in the glaze kiln - this is a real hassle. Same results.

 

I have not tried the method mentioned above, glazing, waiting, glaze again, dry again, glaze. My method has been to glaze all the insides of pots then start with the outside and overlap when the sheen has gone away.

 

The common thread between the 2 pieces is the blue glaze. It is my version of Floating Blue, substitute Gerstley Borate for Boraq. In fact, the grey-blue matt and the reddish glaze both have GB substituted for Boraq. Test tiles did not act this way.

 

The first pic is an overlap Floating Blue over Grey-Blue.  The second pic is Floating Blue by itself.

 

As with everyone else at this time of year, everything to be glazed is "Gotta Have It" for Christmas orders - no screwups allowed.

 

Any ideas as to what occurred and how to fix it?

 

Thank You.

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GB is very plastic so if your glaze has that plus a fair amount of (uncalcined) clay then it could be from glaze shrinkage. Do you have 3134 or 3124? Fritted forms of boron have less problems than GB.

 

I haven't found it necessary to glaze inside then dry overnight before glazing outside unless the pots are very thin. For dipped and poured glazes getting the second coat on as soon as you can handle the pot seems to work best, waiting for the base glaze to dry makes problems.

 

Was the glaze layer overly thick? Any cracking in the glaze before it went into the kiln? Was there any dust on the pots from sanding etc.Maybe post the recipes.

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Min - Thanks for the response. Yes, I do have 3134 and 3124 Frit. The way you glaze is the way I normally glaze. Honestly, I do not remember if there was cracking in the dried glaze before going to the kiln. The glazes may be too thick. In MC6 they state to have the glaze peel off your thumb nail - I have no idea what this is or what it may look like. Perhaps y'all can suggest a better way to gauge glaze viscosity in the bucket.

 

Floating Blue

  Nepheline Syenite...........    50.40    Silica......................    20.20    Boraq.......................    19.50    EP Kaolin...................     3.40    Whiting.....................     3.80    Camadil 95 Dolomite.........     2.70    Ceramic Rutile..............     4.00    Iron Oxide Red..............     2.00    Cobalt Carbonate............     1.50                                =========                                 107.50

Floating Red

  Boraq.......................    37.80    Ball Clay...................     0.70    Magnesium Carbonate.........     8.40    Silica......................    30.10    Whiting.....................     6.00    Iron Oxide Red..............    17.00                                =========                                 100.00

Grey-Blue - I forgot I switched out Boraq for Frit 3195 in the Grey-Blue.

  Ferro Frit 3195.............    12.00    Dolomite....................    14.10    Magnesium Carbonate.........     6.30    Soda Feldspar...............    29.40    G-200 Feldspar..............    10.50    EP Kaolin...................     9.80    Silica......................    18.00    Cobalt Carbonate............     2.05    Rutile......................     6.00                                =========                                 108.15
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The way I read your original post I thought you swapped boraq for GB. There is a fair amount of magnesium carb in the second glaze in particular, it likes to crawl. You could try talc instead, so the recipe would be the same except omit the magnesium carb and add 11.5 talc to replace it and decrease the silica to 23. This keeps everything balanced even though the new total is 96. Do you use a glaze calc program?

 

To measure glaze slurry, getting the right specific gravity for each glaze you use is a good idea until you get to know the glaze well enough to not measure it. Keep the bisque firing the same so it's the same porosity. Put a clear cup on your scale and add water to exactly 100 grams, if you have a graduated cylinder use it instead. Mark a line on the cup where the water comes to and dump it out and thoroughly dry the cup. Now add your glaze slurry up to the line and weigh it. Take this figure and move the decimal 2 positions to the left and that's your specific gravity. Each glaze will have it's own s.g. The idea is to get the s.g. right before each glazing session and dip for the same amount of time so you are laying down the correct amount of glaze thickness. Crawling you had might just be from having too thick a glaze layer. Hope this makes sense.

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Min - Again thanks for the quick reply! Yes, glaze software is DigitalFIre Insight. Will test the change you suggest on the FR glaze. To me, it is a pretty glaze but needs taming. Perhaps this will do it. Wow, so much to learn about glaze. Thanks for the SG example. I like things that are measurable = consistent results - could never measure "glaze peel off your thumbnail".

 

Probably why the test did not mess up is because the glaze slurry was not thick. When a glaze goes to the 5 gallon bucket seems like I lose concept of how thick/ thin it should be. Perhaps treat the test glaze as your SG example suggests to get a base line for each glaze. I do use the MC6 suggestion of 3 ounces of water to every 100 grams dry weight. The Boraq glazes seem to drink up the water, they always take more water than calculated.

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Floating Blue is notoriously problematic. Ask anyone who uses it and they'll all tell you about the strange batch they had that the color was off, or it ran, or it crawled, etc. IMHO, there are much nicer blues out there that are much nicer to work with. Plus there are just so many people who use it. Think about finding a blue that would make your work more unique.

 

As for application, when overlapping glazes, the first glaze should not be totally dry before applying the second layer. If it is dry, it can lose adhesion with the clay and cause crawling. Let the first layer dry until it can be handled, then dip the second layer.

 

The first image looks like it may be too thick.

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Neil - Do you have any suggestions for different blue glazes?

 

That's up to you. Any glaze base can be made blue, so it depends on what you're after. I'm just saying the Floating Blue has been used to death, and your work will stand out more if you're not using a glaze that is so common. Search Pinterest for cone 6 glaze recipes for starters, or do color tests with some other base glazes by adding cobalt in 0.25% increments up to 1%.

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There must be a lot of Floating Blue versions out there.  The one I use is slightly different.

 

Neph Sy       47.3

Gerstley B.  27

Silica            20.3

EPK              5.4

 

RIO                2

Cobalt Carb   1

Rutile              4

Bentonite        2

 

This recipe came with me from the Community Studio where I started.  I became sort of tired of it so I have turned it into Floating Green, which is a nice change.  But I have to say, if I glaze a piece with Floating Blue, it sells.  What's with that??   People like blue I guess!

Roberta

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