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How To Convert Semi-Matte To Glossy Glaze


Saki

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Hi,

 

Attached is an image of a semi-matte glaze called "Variegated Slate Blue" from Mastering Cone 6 Glazes by John Hesselberth and Ron Roy. I love the glaze, but I would also like to find the same glaze with a transparent base—in other words, a glaze that is similar in color and fluidity, but glossy and transparent, instead of semi-matte and opalescent. Is there a way to convert a semi-matte recipe to a glossy, transparent recipe? If that were possible, I think the semi-matte and glossy versions might complement each other well.

 

Any help would be great!

Thanks,
Saki

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Thanks for your reply. I tried that (no slow co, but the result was not much glossier than the photo, and still variegated. I think I may not have properly explained the quality I am looking for. When I refer to a glossy version, I really mean something that is glossy and not "variegated", i.e., I want a glaze that is glossy and smooth/solid, without the "opalescent" quality. The teal glaze on the rim of the cup in the photo below has the transparent/glossy/non-variegated quality I desire. For contrast, the red glaze on the honey pot in the other photo here is glossy, but variegated. I am not sure I am using the terminology correctly, but I hope that this makes sense. If I am not being clear, please let me know.

 

Thank you!

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In stead of trying to change a glaze that (in my opinion) derives its character from crystallization, why not start with a glaze that is designed to be glossy?  Then you can experiment with adding colorants until you get the hue you want.  This would still allow you to use the original glaze in combination with the glossy glaze.

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Look up green celadons. That is the glaze type your looking for.

 

In stead of trying to change a glaze that (in my opinion) derives its character from crystallization, why not start with a glaze that is designed to be glossy?  Then you can experiment with adding colorants until you get the hue you want.  This would still allow you to use the original glaze in combination with the glossy glaze.

 

Thanks. I am definitely be open to trying these approaches!

 

Joseph: If I find a celadon base, could I get the same color as in Variegated Slate Blue just by using the same colorants?  Are there other adjustments I would need to make?

 

Ray: My (very rudimentary) understanding is that colorants behave differently in different base glazes, so using the same colorants in a glossy base glaze won't result in the same color as the semi-matte base glaze base. I was just hoping that if it is possible to make a minor adjustment to the semi-matte glaze, then the colorants would still behave similarly. By contrast, my concern with starting from a completely different glossy glaze is that I wouldn't be able to make a green that is compatible/complementary to the one in the photo. But maybe my thinking is way off?

 

Thanks again for your help,

Saki

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Nothing is ever going to be that exact in glaze chemistry unless you get lucky.

 

You could start with the same colorants and go from there.

 

If I was you I would start with finding a good celadon base for your clay body. Then once you find one that works well start making test batches with colorants and tweak until you find what your looking for.

 

That transparent look is not easy to achieve without a lot of testing, but not much is easy in this field.

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I mean don't get me wrong it's not impossibly hard or anything. It is just recipes don't really go from potter to potter with the same looks that often. We can sit here and list 100's of glaze recipes and you could try them all. But the sure fire way to find what you want is to start with a base and then move outward once you find a transparent that fits your body well. Atleast after you do all this you will understand what you need to do to make the changes you want each time.

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The slate blue variegation is from the rutile in the recipe and I think the reds variegation is probably from high boron. Remove the rutile and you might get something close to the glaze you want. Looking pretty glossy to me already. If it is still a little dull you can tinker with silica to alumina ratio to go towards a better gloss.

 

Also can use any base glaze you are happy with and try different cobalt/copper values. There is more to how the final glaze looks than purely recipe.

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Saki, just to add a bit.  It's true that different oxides will influence color, but you can get almost any color you want with a glossy glaze, especially if you're working midrange, especially in the green to blue spectrum.  For example, the following glaze appears to be a celadon, but is actually an oxidation glaze using chartreuse and turquoise glaze stains.

 

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I feel the 1.5% cobalt carbonate is also a little too much from my experience for the subtle blue. Something <= 0.5%

 

I can't remember for sure but I think this test tile of mine only used a max 0.5 cobalt, but I am not 100% The copper I think again went up to 1.5% max with them 'cross blending' to a transparent glossy glaze bottom left corner. Ignore my spotty cobalt, it is a little weird and needs blending better.

 

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Thanks for your reply. I tried that (no slow co, but the result was not much glossier than the photo, and still variegated. I think I may not have properly explained the quality I am looking for. When I refer to a glossy version, I really mean something that is glossy and not "variegated", i.e., I want a glaze that is glossy and smooth/solid, without the "opalescent" quality. The teal glaze on the rim of the cup in the photo below has the transparent/glossy/non-variegated quality I desire. For contrast, the red glaze on the honey pot in the other photo here is glossy, but variegated. I am not sure I am using the terminology correctly, but I hope that this makes sense. If I am not being clear, please let me know.

 

Thank you!

The teal is likely a semi-matte with a clear glaze over it. My guess is the semi-matte has enough copper to leach and the clear is used to seal the copper. If you just want the glossy teal glaze, find a good clear glossy glaze and add some green or teal mason stain to it.

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if you find a simple clear or transparent glaze that works well on your clay, you can add colorants to it and making many different colors.  do not add rutile since that is what the streaky effect is in the original post.

 

carbonates are simpler than some oxides.  i don't know the chemistry but the tests above show speckling of colors.  that is what i always get with oxides but carbonates do not seem to do this, there are no dark speckles, just even color.  

 

this is not a simple process, nothing about working with ceramics is easy, it is sometimes two steps forward, one back.  or the reverse.

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I would love to be able to share it, but my kiln room, where I kept my notebooks, was damaged in a storm and the notebooks got soaked.  I didn't notice until they were compost, and so I no longer have the formula for that glaze, just a half-empty bucket of it.

 

But I recall that it was a fairly simple gloss glaze, relying on a classic balance of the usual suspects, aided by a bit of gerstley borate.  I also recall that the color was developed by experimenting with  different proportions of two mason stains-- turquoise and chartreuse.

 

I'll have to work out a similar glaze eventually, and I'd be happy to post it then.  It is a Cone 8 glaze, but would probably be fine for 6 with a bit more boron.  It could probably be adapted for single firing too, as I refuse to use glazes that do not contain a reasonable amount of alumina in the form of clay.

 

I'll bet that if you have a zinc-free clear gloss that moves a little in the firing, you could easily duplicate the effect.  I might start with 3% turquoise and 5% chartreuse. 

 

A double line blend would probably get you pretty close in short order.

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The slate blue variegation is from the rutile in the recipe and I think the reds variegation is probably from high boron. Remove the rutile and you might get something close to the glaze you want. Looking pretty glossy to me already. If it is still a little dull you can tinker with silica to alumina ratio to go towards a better gloss.

 

Also can use any base glaze you are happy with and try different cobalt/copper values. There is more to how the final glaze looks than purely recipe.

Thanks, I think I might try both options. (removing rutile and looking for a new base glaze)

 

I feel the 1.5% cobalt carbonate is also a little too much from my experience for the subtle blue. Something <= 0.5%

 

I can't remember for sure but I think this test tile of mine only used a max 0.5 cobalt, but I am not 100% The copper I think again went up to 1.5% max with them 'cross blending' to a transparent glossy glaze bottom left corner. Ignore my spotty cobalt, it is a little weird and needs blending better.

This is very helpful. Thank you.

 

The teal is likely a semi-matte with a clear glaze over it. My guess is the semi-matte has enough copper to leach and the clear is used to seal the copper. If you just want the glossy teal glaze, find a good clear glossy glaze and add some green or teal mason stain to it.

 

Fascinating. I hadn't realized that putting a clear on top of a semi-matte could remove some of the variegation. I might try experimenting with that. But your suggestion to look for a clear glossy base and then add colorants seems to be the consensus. The Hesselberth and Roy book includes 2 glossy base glaze recipes, so I guess I will start there. Thank you.

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thank you, ray.  sorry for the loss of your notes.  hope nothing else was much damaged.  will try the suggestions you made.  i never use a glaze that runs so it might be a little difficult for me to adjust my thinking that it is ok.  i like the color of my "turquoise" glaze but it is made with Cerulean Mason stain.  the recipe is Bill vanGilder's Rutile Green but without the copper.  it has some lovely effects from the rutile.

 

 will have to get some turquoise and some chartreuse mason stains.

 

FYI i use a cone 8 glaze occasionally at cone 6.  the Chinese Red that has rio in it and that i complain about is a cone 8 recipe from Jane Cullum of Manassas Clay.  it is spectacular in sunlight.

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The storm got some of my chemicals, but otherwise it was okay.  I was pretty sad about the notebooks, since I'd been keeping them since about 1972. 

 

You won't need a fluid glaze, just one with enough movement to settle into recesses, and collect a little on horizontal edges.  I would guess that a Cone 6 celadon recipe without the iron would make a good starting place for a base glaze.

 

We're about to head north for the summer, and one of the projects is to set up a little studio in a pre-fabbed shed on our acreage.  Wish me luck.

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