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Soren

Staining Amaco versa clay #20 Body

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Recently, I have been trying to use stains and oxides to color the clay I use.  As a complete ceramics beginner, I may be tackling more than I should, but I am an engineer by trade, so the experimentation is a draw for me.

I hand-build, sometimes using a press mold.

My preferred clay at this time is Amaco versa clay #20 that I bisque fire to Cone 04 and glaze fire to Cone 06.

I have made some small (~1kg) batches of stained body clay and test fired small disks with different concentrations of stain.  For some reason, even with concentrations of 10 to 2 (sometimes even 10 to 3) the colors almost always appear washed out and pastel.  I expected this somewhat from adding stain to the clay body, but it seems like I would be adding much more stain than I normally read in recipes if I increase my concentrations to obtain darker colors.

Is there a better way to obtain bold colors in clay bodies?  With the way I calculate the concentration, I am using a comparative ratio rather than a percentage.  I first measure out 1000 grams of clay and add 200 grams of stain to obtain a concentration of 10 to 2 (that I note as 20 or "20%" which is not a true percentage, as actual percentage is 2/(10 clay+2 stain)=16.67%).  Would it be problematic to increase the percentages higher than true 20%?

One colorant in particular that I used was cobalt carbonate.  I have read that this is a strong colorant and will produce dark blues at concentrations of 1-5%.  At my concentration of 10 to 2 (16.67% stain), the color was still only medium blue.  I have ordered some cobalt oxide to test instead of cobalt carbonate, and I hope this helps in obtaining a dark blue with the Amaco #20 clay.

Are my problems possibly also resulting from the use of earthenware clay?  I have read that colorants are usually bolder when fired to higher temperatures, as long as they do not burn out.  Earthenware is preferred for the products I make due to the porous nature allowing for moisture absorption, so I do not want to switch to stoneware.  It may be that staining the clay I use will not work if I want dark colors.

Another strange observation was with Mason Stain  #68194 Scarlett Red (may be discontinued).  Even with a ratio of 10 clay to 3 stain (23% stain), the clay appears to have only the very faintest bit of pink tint after test firing, almost without color effect.  The unfired clay has a noted medium pink tint over the gray clay that disappears during firing.  Why might this stain tint be disappearing when fired to cone 04?

Any help is appreciated.

Thanks,

Soren

Edited by Soren
I use a press mold, not a slump mold like previously mentioned

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I have not worked with your exact clays and did fire at a higher temp.  But when I used mason stains with the clay, they needed a clear glaze to make the colors come alive.  

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12 minutes ago, lgusten said:

...they needed a clear glaze to make the colors come alive.  

Thanks for the advice, lgusten.  I intended to test with a clear glaze, but have not yet added the glaze to my test disks.  I really need to do this.

In some cases, this may help, but I also would like to try burnishing or terra sigillata instead of glaze for the surface effects they give.  This would eliminate any benefits obtained from clear glazing.

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Soren:

amaco versa clay is a dark body: wrong choice for colorants. Look at Standards 100 or 105 for a starting point. Typically white porcelain is used for colored clays: requires much less colorants.  Below is a colored 04 porcelain frit ware, with clear glaze. The color bands are inlaid colored clay as well. Chris Campbell and I have been discussing uses at 04. She is an exceptional artist, I just develop clay bodies. 

gallery_73441_1183_1139200.jpg

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This clay body, Amaco Versa Clay No. 20,  appears to be similar to a low fire clay I used when I was first introduced to ceramics.  

The clay I used (Armadillo Long Horn White) is a talc based clay body that is grey in the bag, and fires to a very bright white at temperatures above cone 08 (which is our bisque temperature at school).   I fired it at cone 3 in an oxidation gas kiln and it responds well to cobalt , copper, and iron glazes at cone 3.    I also used it for raku and it produces good colors there.   I also use this clay as a slip glaze for the exterior of bowls made with dark firing clays at cone 10.    My comparison with porcelains is that it is a brighter white fired at bisque and at cone 3 than the popular porcelains fired to cone 6 and cone 10 reduction.      

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Thanks for the replies, glazenerd and Magnolia Mud Research.

14 hours ago, glazenerd said:

Look at Standards 100 or 105 for a starting point. Typically white porcelain is used for colored clays: requires much less colorants.  Below is a colored 04 porcelain frit ware, with clear glaze. The color bands are inlaid colored clay as well. Chris Campbell and I have been discussing uses at 04. She is an exceptional artist, I just develop clay bodies. 

Is 100 Artist White clay quite porous after bisque firing to cone 04?  Would it have properties similar to the Amaco Versa Clay #20, such as higher plasticity and bright white color at cone 04?  I will have to order some of this to try it with colorants.

All of my clay work at this time is with low-fire clays to have high porosity after bisque firing to cone 04.  I am not familiar with porcelain frit ware.  Is this a type of low-fire porcelain?  Would it have high enough porosity to absorb moisture after bisque firing to cone 04?  I mostly make ocarinas when I have time to spend with ceramics, and moisture from breath needs to be absorbed by the fired clay while playing to avoid condensation issues.  I will try to get in touch with Chris to further develop my understanding of what I might be capable of obtaining with my criteria.

Out of curiosity, what differentiates porcelain from earthenware?  I was under the impression that porcelains were high-fire (cone 8 to cone 10 or higher) and were more difficult to work with than earthenware.

13 hours ago, Magnolia Mud Research said:

The clay I used (Armadillo Long Horn White) is a talc based clay body that is grey in the bag, and fires to a very bright white at temperatures above cone 08 (which is our bisque temperature at school).   I fired it at cone 3 in an oxidation gas kiln and it responds well to cobalt , copper, and iron glazes at cone 3.    I also used it for raku and it produces good colors there.   I also use this clay as a slip glaze for the exterior of bowls made with dark firing clays at cone 10.    My comparison with porcelains is that it is a brighter white fired at bisque and at cone 3 than the popular porcelains fired to cone 6 and cone 10 reduction.      

Bright white is what I was looking for when I came across the Amaco Versa Clay #20.  Porosity and water absorption is of great benefit to the ceramic work I do (as mentioned just above), so I would like to stay within the earthenware/low-fire range.  The kilns I have are all electric with indirect venting, so I may have to look more into venting in order for better colors.  I am suspecting that my experimentation confirms what glazenerd mentioned, in that the Amaco #20 is a dark body, and therefore is inhibiting to the use of colorants.  The pastel colors are still quite nice, but I will probably look to a different clay in order to achieve dark colors.  I really like the properties of the Amaco #20 for my work, including the bright white color when fired to cone 04, but there are probably better clays available to add body color.  The Amaco #20 can still be colored using colored glazes.

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2 minutes ago, Callie Beller Diesel said:

You mentioned wanting to experiment with terra sig. Colouring that, rather than your clay body might give you the colour response you’re looking for while keeping the porosity of the clay. 

This is definitely something I would like to try, and colouring the terra sig would certainly be easier than body colouring.  For the ocarinas I make, terra sig might provide a surface finish that is durable but does not prevent finger movements as much as the grip of gloss glaze.  I also may try to use a burnished surface or matte/satin glaze for this same effect.

Terra sig is not an option for some things I would like to try, though, such as agateware or marbling, as the effect would be covered by the terra sig.  Agateware and marbling are my main interest in clay body coloring.

I have considered trying a thin agatware layer made with colored porcelain over an earthenware form, but this seems too overly difficult just to maintain porosity.  Matching the layers to fire properly and not separate or crack seems a risky and daunting task for a product like an ocarina that requires hours of time to produce.  My considerations are generally different than those of a potter and probably more similar to a sculptor due to the time input and potential value of each single ocarina.

At this point, I am finding that I cannot try everything I would like, as I am a ceramicist by hobby and an engineer by trade.  My vacation from work is to stay at home and work clay.  Too much concentrated method experimentation/engineering in my hobby makes it less relaxing and interesting, so I should probably just focus on a few finish methods.  This leaves me unsure of when or if I will get into terra sig...

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I think perhaps that the amount of porosity you want in your ocarinas can be achieved by brushing or spraying a light coat of clear glaze over the outside of the piece, leaving the inside unglazed. Or alternately, a light spray of soda ash or other flux dissolved in water. Something with just enough flux to brighten the colours of the agate ware up, but not enough to seal the piece completely. 

And don't be afraid of terra sig. It's easy and pretty fun to make, if you're a fan of the sort of kids' science experiments you can do at home. Marcia Selsor has a most excellent method that involves a pop bottle. If you're using stains to colour sig made in this fashion, be sure to add the stain after you decant your sig. The particles are relatively heavy and will wind up in the bottom layer that you discard. 

https://www.marciaselsorstudio.com/how-to-make-terra-sigillatta.html

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1 hour ago, Callie Beller Diesel said:

I think perhaps that the amount of porosity you want in your ocarinas can be achieved by brushing or spraying a light coat of clear glaze over the outside of the piece, leaving the inside unglazed.

This is how I currently do it, brushing on the glaze.  The reason I might consider different surface finish is to avoid the cling that gloss glazes have to fingers or lips which are inhibiting to movement.  The inside of the chamber should have more than enough absorption that condensation should not be an issue with an earthenware ocarina.

Thanks for the terra sig reference.  I will probably make use of this at some point when I find the time.

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From a safety standpoint, folks should not be putting their mouths on an unglazed surface that has a bunch of oxides/stainds in it that aren't sealed off by a good glaze.

Not all glossy glazes have the same feel to them. Some are grippy, some are less so. A satin or matte glaze would definitely be less grippy.

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7 minutes ago, neilestrick said:

From a safety standpoint, folks should not be putting their mouths on an unglazed surface that has a bunch of oxides/stainds in it that aren't sealed off by a good glaze.

Not all glossy glazes have the same feel to them. Some are grippy, some are less so. A satin or matte glaze would definitely be less grippy.

Thanks for the tip, Neil.  I definitely have taken the safety into consideration, and would either glaze the mouthpiece or use an unstained clay for the mouthpiece.

Satin and matte glazes are something I am also considering, so I am glad you recommend them if I want less cling on the surface.

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