Jump to content
Linda Lees

Black on Black Firing

Recommended Posts

Hello,

I recently came across a couple of YouTube clips on a firing method used by Pueblo people of the Southwest USA. There appears to be a couple of bits of information that aren't quite clear. If anyone has attempted this type of firing, I'd love some guidance. I made some small pots using earthenware terracotta clay. Four of the pots had terra sigillata made from the same clay applied to them and one I burnished using the back of a spoon. I then bisque fired the pieces, this is the step that I'm not sure I should have done. Several days after the bisque, I applied patterns onto the pots using iron oxide. On the first three I added the oxide to the terra sig and painted it on. The pieces were then placed in a wheel rim, surrounded with sawdust pellets and a metal barbecue plate placed on top. Around this I placed lots of fire wood. I kept the fire burning hot for about three hours. All of this had been done in my pit, and after the three hours I placed sheets of iron on top of the pit to retain the heat. The results were ok, but not what I was after. The pots were a dark brown, not black, and the shine and matte areas were a bit all over the place. The idea is that the areas that are burnished stay glossy and the areas where the oxide is applied should be matte. I had two pots left so I painted the design on these using iron oxide in slip. These pots were placed in a tin, completely covered in sawdust, the barbecue plate placed on top and fired as above. The results for these was much the same as for the first three pots. 

What I'd like to know is - Should I be bisque firing first?  What is best for painting on the design?  

I did try to contact on of the people from the video, he is a university tutor, but I've not yet received a reply. I've attached a couple of photos, the first one had terra sigillata applied, the second was the one I burnished with a spoon.

Any advice gratefully accepted,

thanks, Linda

3c small.jpg831384677_IMG_0707small.jpg.e536b20ac1e71139b687f625dca485b4.jpg

 

Edited by Linda Lees
photo too big

Share this post


Link to post
Share on other sites

Marcia Selsor of this forum does / did a lot with terrsa sigs search terra sig in these forums and you may get a few clues...thickness of application, burnishing.

Temps etc

Burnishing patchy could mean need to apply a thicker coat prior to burnishing or hot spots  burning off the sheen....

Those folk been doing it for centuries remember:-)))

Share this post


Link to post
Share on other sites

Thanks Babs. Hi Linda. I have used the San Ildefonso process in teaching many years ago. Basically, you burnish the pot . Then , before bisque firing, paint the patterns over the smooth finish with a type of terra sig. Ball clay based TS works.   It looks like your clay is a little rough. What are you using?

If you could find a tempered earthenware that is smooth but has fine grog, you would get a smoother surface. The pot on the right looks smoother but has a little color showing. Bisque to ^08.  Do you have access to dried cow pies (frisbee quality manure)? We used this in some large pits intermixed with sawdust. Smothered with sawdust towards the top of the pit . Once the flame appears at the top, we covered with more sawdust and sheet metal or corrugated metal and let it smoke and cool. 

Hope this helps.

Marcia

Share this post


Link to post
Share on other sites

Thanks for your response Marcia. I live in a rural area and get my clay through a ceramics club of which I'm a member. The club no longer buys earthenware clay after a couple of accidents where it was fired to stoneware. I was given a small amount of terracotta earthenware that I used for these pots. The one on the right was burnished with a spoon, that's how it has a smoother finish. Three of the pots were burnished using a terra sigillata made from the same earthenware clay. One was burnished with a  spoon and on the last one I applied a terra sig made from a white ball clay. In the first firing, for the pattern, I added iron oxide to the terra sig. When this didn't show up very much I used a slip with iron oxide for the pattern in the second firing.  I had the pots buried in sawdust right from the start of the firing, is this correct? Or should I wait to add the sawdust?  In your firing, did  the sawdust come in contact with the pots? The pots were bisque fired to 06.

I'm out of earthenware clay, so I've made another couple of stoneware pots from a smooth clay. I've burnished with a spoon and intend also using terra sig made with ball clay. I've gotten some stable manure which contains a lot of sawdust. I was going to try doing the firing without first bisque firing. Hopefully, with a smoother surface, the results might not be as patchy. I'll try firing again on Saturday (Australian time). I'll post the results here.

Share this post


Link to post
Share on other sites

Horse manure has more nitrogen. The Quezadas use it when they fire individual pots under a small bucket.  

There is no need to add iron to the over slip terra sig. It's absorbency allows the carbon to turn the pots black.

Marcia

Share this post


Link to post
Share on other sites

These are the results of my second firing. The pots were not first bisque fired. I spent a lot of time burnishing with a stone and then using terra sigillata. I buffed the sig with a plastic bag before painting on a design, also with terra sigillata, but not burnishing this.  I built a small fire and tried to get it really hot. I had the pots sitting by the fire to warm them prior to placing the metal tin on top of the fire, with the pots sitting inside, on a bed of cow manure. I then buried the pots in more manure inside the tin, placed a barbecue plate on top and piled up more wood around it. I kept it burning quite hot for a couple of hours. Measuring the temperature using an infrared thermometer that has an upper limit of 550 degrees celsius (1022 f) it exceeded the limit of the thermometer, giving me a reading of High.  After leaving it all to cool down for several hours I removed the pots. As you can see, they were quite glossy, however, they have metallic spots across them. When cleaning the pots, I decided to see if the metallic areas were fixed, or if they would wash off. As you can see in the second picture, the sheen was also removed.  Another thing that happened during the firing was that the bottom blew out of one pot and the other had small, raised dimples across the base. I'm assuming that this is from too much direct heat, perhaps I should have had a fire brick or piece of kiln shelf inside the tin for the pots to sit on? 

 

IMG_0849small.jpg

IMG_0850 small.jpg

IMG_0851 small.jpg

IMG_0852 small.jpg

IMG_0854 small.jpg

Share this post


Link to post
Share on other sites

Bottom photo may be due to not quite dry pot prior to firing. Moisturw can cause explosive blow outs.

The fast range of temp up and down can ruin pots if clay body not robust enough but dobt thin that is the case 

Lovely pots!

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.