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Mossyrock

Terra Sig Not Buffing Shiny

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I'm asking this for a friend who is not on the computer.  She makes her own terra sig out of Red Art and her pottery is made using Highwater Clay's Stans Red clay.  The sig buffs up beautifully if applied straight to the Stans Red on bone dry pieces.  She recently started covering her leather hard pieces with a white slip (pieces are majolica decorated), then, after bisquing, glazes with her regular base glaze before applying the majolica colors.  

 

In her last session of making pieces, she wanted the bases of her mugs and vases to have a black terra sig instead of the red sig so she added black stain to it.  It was applied on the bottoms of bone dry pieces that also had had slip applied.  The color came out a beautiful black, but no matter how many layers, or how hard or long it was buffed, it would not form a sheen.  On the final fired pieces the black terra sig is a very matt black.  Is this because it is being applied over slip?  Aside from adding the black stain, the addition of the slip is the only difference.

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My experience with siggy is consistent with Neil's assessment. Adding stain colorants to siggy is less than successful because the typical grain size of stain is much coarser than the very finest clay particles in TS. Some have reported that ball milling the stained siggy improves it, but I haven't tried that. I have also tinted siggy with cobalt or copper carbonate. As fine as those are, they also are coarser than the clay fines in the siggy, but not as bad as stains.

 

You don't say how hot your colleague glaze fires, but note than even plain TS which may appear to still be somewhat shiny after bisque will not be shiny anymore when fired above cone 1. That may contribute to the matte appearance of the otherwise uncoated bases.

 

I don't think the slip would make a difference as long as it is applied smoothly. One caveat I give when presenting TS techniques to my classes is that siggy sure is shiny, but it can't cover and fill in bad finishing of the underlying surface.

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It's almost certainly the size of the stain particles, as per Dick and Neil's responses.

I do have a suggestion, depending on the final temperature your friend fires to.

I use a terra sig on the foot-rings and lid galleries of my majolica - I like the silky sheen it gives, and it helps seal the otherwise still porous body. The clay body I use is red, but the sig is made from a white-firing ball clay. After biscuiting, the sig remains a grubby white, but after glaze firing it has taken on the colour of the body - a gorgeous smooth red, with no sign of white or milkiness.

It could then be worth your friend staining the slip under the sig, rather than the sig itself. This might depend on the temp fired to - I glaze fire to cone 03 well and truly down, so 1105 deg C (2014 deg F) ++.

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I think it is the stain as well, but it could be the slip applied. I had a handout from decades ago from an artist who did add stain to terra sig. There really isn't a need for the white slip if she is using majolica glaze. It is opaque enough to cover earthenware.

Marcia

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If I use slips or Terra sigs they're applied when the vessel is leather hard, other wise the bone dry surface zaps the moisture out making it hard to shine.

 

I have experimented mixing mineral oils and vegetable oils in and on clay bodies to

slow down the drying rates.

 

Alabama

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Thanks for the help everyone.  After reading the comments, I believe it is probably the addition of the stain that has made the sig "unbuffable".  If that's the case, how can she get a black sig?  I know I've seen it used on other potter's pieces.  She bisques to Cone 04 and glazes to Cone 05.  

 

The reason she started applying white slip to the Stans Red clay was to save on the base glaze.  She only had to apply one coat (brushed on) of the base white glaze if the slip was on the piece.  Otherwise she had to wait until the glaze dried then brush on another coat.  She uses Stroke & Coat as her decorating glazes.

 

Need to do a little experimenting......try the black sig on a test piece...... slip applied only to part of it and apply the sig across both areas.  See what happens.

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I use a terra sig on the foot-rings and lid galleries of my majolica - I like the silky sheen it gives, and it helps seal the otherwise still porous body. The clay body I use is red, but the sig is made from a white-firing ball clay. After biscuiting, the sig remains a grubby white, but after glaze firing it has taken on the colour of the body - a gorgeous smooth red, with no sign of white or milkiness.

It could then be worth your friend staining the slip under the sig, rather than the sig itself. This might depend on the temp fired to - I glaze fire to cone 03 well and truly down, so 1105 deg C (2014 deg F) ++.

Are you saying that after the glaze firing, the white sig you're using takes on whatever color it is applied over?  Say if it was applied over a green underglaze, the sig would be green after it was glaze-fired?  If that is the case, would you mind sharing which ball clay you use or do you think any would work?  She glaze fires to 05.

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Are you saying that after the glaze firing, the white sig you're using takes on whatever color it is applied over?  Say if it was applied over a green underglaze, the sig would be green after it was glaze-fired?  If that is the case, would you mind sharing which ball clay you use or do you think any would work?  She glaze fires to 05.

 

 

 

Yes, that's what I'm saying. Certainly, it does so over red clay body when fired to cone 03, and I can see no reason that it wouldn't do the same over a coloured slip. Well worth some experimentation, I would suggest. I always apply the sig to a bone dry body.

The ball clay I use is something called Hyplas 71, but then I'm in Europe. That may or may not be available on your side of the pond. Essentially, it's a low-iron, white firing, high plasticity ball clay. I doubt if the exact make/type matters much, to be honest. I've always followed the Vince Pitelka method for making sig, but again, I doubt if that makes any difference to the end result.

My only concern might be that cone 05 could be a little low to lose the milkiness of the sig - only one way to find out!

 

--->> It's just occurred to me to suggest that your friend decants a small amount of sig into a cup before trying this, in case the brush takes up some of the (dry) stained slip, and transfers it back to the sig - you don't want to ruin a batch of sig with stained slip dust!! (Does that make sense? I think so...)

Edited by Sputty

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Are you saying that after the glaze firing, the white sig you're using takes on whatever color it is applied over?  Say if it was applied over a green underglaze, the sig would be green after it was glaze-fired?  If that is the case, would you mind sharing which ball clay you use or do you think any would work?  She glaze fires to 05.

 

 

 

Yes, that's what I'm saying. Certainly, it does so over red clay body when fired to cone 03, and I can see no reason that it wouldn't do the same over a coloured slip. Well worth some experimentation, I would suggest. I always apply the sig to a bone dry body.

The ball clay I use is something called Hyplas 71, but then I'm in Europe. That may or may not be available on your side of the pond. Essentially, it's a low-iron, white firing, high plasticity ball clay. I doubt if the exact make/type matters much, to be honest. I've always followed the Vince Pitelka method for making sig, but again, I doubt if that makes any difference to the end result.

My only concern might be that cone 05 could be a little low to lose the milkiness of the sig - only one way to find out!

 

--->> It's just occurred to me to suggest that your friend decants a small amount of sig into a cup before trying this, in case the brush takes up some of the (dry) stained slip, and transfers it back to the sig - you don't want to ruin a batch of sig with stained slip dust!! (Does that make sense? I think so...)

 

Thank you!  It's definitely worth a try.  I'll see if I can find a similar ball clay and run a few experiments.

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As I am preparing for a yard sale and packing my studio, I found a different article from CM on Terra sig. It includes Christine Federighi's terra sig recipes.

She suggested ball milling the stain in with the terra sig OR add it after the Terra sig settles. There are many recipes without stain but with metal oxides.There are 3 pages of recipes , some are for terra sig.

 

Marcia

woodyHughes.pdfwoodyHughes 1.pdfwoodyHughes 2.pdf

woodyHughes.pdf

woodyHughes 1.pdf

woodyHughes 2.pdf

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Mossy rock,

I hope you read the above post. It seemed to disappear right after I posted it.There is a lot of good information in those 3 pages even if they date back to 1993.

 

Marcia

Thank you Marcia.  I will read definitely read and thank you for taking the time to post them.

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When I first started out in primitive pottery, one of my interests was Terra sigellatas and iron oxides. An advanced student, Michael Hansen, showed how to make Terra Sig. He was a former student of Curt Wilder. His method was:

 

1. Collect about a cup - cup and a half of wood ash.

 

2. Dig up some type of red dirt/clay that you think want to try.

 

3. Wait til the archaeology professor goes to class, and take his Mr. Coffee grounds basket off. Place a coffee filter inside and fill with ash.

 

4. Place the basket over a jar and pour water thru the ash. The liquid will look like apple juice.

 

5. Take the dirt sample and add a lot of water. Stir or shake til its all dissolved.

 

6. Pour into a tall(preferably glass) cylinder, then add 2-3 tablespoons of the ash liquid (lye). This seems to release the magnetic properties of clay. Leave it sit for 24-48 hours. With glass you can see the stratified layers. Pour off the water, and scoop off the top layer...that is the Terra Sig.

 

If the slip starts to flake off, add some of your clay to the terra sig so the shrinkage rate will be compatible.

 

The top layer of Terra Sig will only be 1/4 inch...the stratified layers will be according to particle size...gravel on the bottom, sand, grit, etc

 

7. Put coffee pot back together, without the ash!!!

 

Seeya,

Alabama

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