AnaLucia Posted March 28, 2018 Report Share Posted March 28, 2018 Hi, I am new to this forum and if possible, would like to have some advice. I fired a group of sculptures on my new electric kiln (third fire), and most of them have come out with 'white spots'. I am attaching photos so you can see them. I bisque fired them them to 1000 c The clay I used was: Valentine Clays. ES 180 Sculpting/Pizza Clay. I wonder if it is the clay or the temperature of the kiln. Any advice? Link to comment Share on other sites More sharing options...
Fred Sweet Posted March 28, 2018 Report Share Posted March 28, 2018 AnaLucia- if you are referring to the small round shapes, that is probably the corderite grog. If you are talking about a whitish “haze” that may be scumming from a trace soluble salts, fr either your clay or water, migrating to the surface as the piece dries. This is something that the clay producer will have to address when they make the clay body. regards, Fred Link to comment Share on other sites More sharing options...
Min Posted March 28, 2018 Report Share Posted March 28, 2018 +1 for what Fred said about the haze being from soluble salts. Doesn't look like they are adding barium to the clay to help prevent the issue. https://www.valentineclays.co.uk/sites/default/files/Technical Information.pdf Link to comment Share on other sites More sharing options...
The Duck Barn Artisan Posted March 28, 2018 Report Share Posted March 28, 2018 Agreed as above and although I havent used this clay myself, I know this clay has a range of 950 -1300. it may be that the bisque firing was at the lower end. If you were not intending to glaze then maybe do a test firing at the higher end and see if that makes a difference. I had a similar thing happen to me when I fired some E40 with my usual buff clay (bisqued @ 1040c) and instead of coming out a white colour it was pink due to the firing being low. Kindest regards, Shel. Link to comment Share on other sites More sharing options...
Magnolia Mud Research Posted March 28, 2018 Report Share Posted March 28, 2018 The important question is what did you plan to do after the bisque firing? What finishing technique was planned? If the piece was to be stained or glazed and fired to a higher temperature, go ahead and do that. If the bisqued firing was intended to be the only firing, then the issue of surface color of the bisque may be more than just an educational artifact. I have noticed with some bisqued clay bodies that washing of the bisque ware with tap water and allowing it to dry will change the surface color somewhat. Don't know why. LT Link to comment Share on other sites More sharing options...
AnaLucia Posted March 28, 2018 Author Report Share Posted March 28, 2018 1 hour ago, Fred Sweet said: AnaLucia- if you are referring to the small round shapes, that is probably the corderite grog. If you are talking about a whitish “haze” that may be scumming from a trace soluble salts, fr either your clay or water, migrating to the surface as the piece dries. This is something that the clay producer will have to address when they make the clay body. regards, Fred Thank you Fred! I have read somewhere else that it could be the clay which is not good news as I have bought a few kilos. I also thing that it may be that I didn't fire the pieces at a high enough temperature.... Thank you very much for taking the time to answer! Link to comment Share on other sites More sharing options...
AnaLucia Posted March 28, 2018 Author Report Share Posted March 28, 2018 1 hour ago, Min said: +1 for what Fred said about the haze being from soluble salts. Doesn't look like they are adding barium to the clay to help prevent the issue. https://www.valentineclays.co.uk/sites/default/files/Technical Information.pdf In that case, I will come back to the place I bought the clay and raise the issue.... Thank you for your help! Link to comment Share on other sites More sharing options...
AnaLucia Posted March 28, 2018 Author Report Share Posted March 28, 2018 1 hour ago, The Duck Barn Artisan said: Agreed as above and although I havent used this clay myself, I know this clay has a range of 950 -1300. it may be that the bisque firing was at the lower end. If you were not intending to glaze then maybe do a test firing at the higher end and see if that makes a difference. I had a similar thing happen to me when I fired some E40 with my usual buff clay (bisqued @ 1040c) and instead of coming out a white colour it was pink due to the firing being low. Kindest regards, Shel. I am very very new to firing my own pieces and I have the impression that you are right. I will try firing them at a higher temperature and see... Thank you very much! Link to comment Share on other sites More sharing options...
AnaLucia Posted March 28, 2018 Author Report Share Posted March 28, 2018 1 hour ago, Magnolia Mud Research said: The important question is what did you plan to do after the bisque firing? What finishing technique was planned? If the piece was to be stained or glazed and fired to a higher temperature, go ahead and do that. If the bisqued firing was intended to be the only firing, then the issue of surface color of the bisque may be more than just an educational artifact. I have noticed with some bisqued clay bodies that washing of the bisque ware with tap water and allowing it to dry will change the surface color somewhat. Don't know why. LT I intended to do just one firing and I think now that I should have fired it at a higher temperature. Could I put the pieces back without any glaze or stain and re fired them? Thank you for your help. Is my first time in this Forum and I am so grateful for the support! Link to comment Share on other sites More sharing options...
Magnolia Mud Research Posted March 28, 2018 Report Share Posted March 28, 2018 Yes, you can refire to a higher temperature. You might talk to the clay supplier about the color changes as the firing temperature is increased. My suggestion is to make several 'test pieces'; small - say the size of your fist. Fire each one to a different higher temperature; this will give you information of the surface appearance after firing. Then on the basis of the testing, you can choose the firing temperature for your initial piece. From another approach, there are lots of ways to treat the surface of sculpture. Many of my sculptural pieces are intended for controlled environments (kept in the house or barn) and after the bisque firing, the pieces are rubbed with a thin coating of raw moist clay - different naturally colored clays provides a palette similar to earth-tone chalk used in drawings. Applied carefully, the surface does not flake. There are many 'dry glaze/stain' alternate approaches (relative to glazes, etc.) for sculptural ceramics. LT Link to comment Share on other sites More sharing options...
Rae Reich Posted March 28, 2018 Report Share Posted March 28, 2018 Sometimes my bisque fired pieces have had "bleached" looking areas, but it was never a problem since I glazed them. I always assumed that it was caused by proximity to the heat source. Link to comment Share on other sites More sharing options...
AnaLucia Posted March 28, 2018 Author Report Share Posted March 28, 2018 1 hour ago, Magnolia Mud Research said: Yes, you can refire to a higher temperature. You might talk to the clay supplier about the color changes as the firing temperature is increased. My suggestion is to make several 'test pieces'; small - say the size of your fist. Fire each one to a different higher temperature; this will give you information of the surface appearance after firing. Then on the basis of the testing, you can choose the firing temperature for your initial piece. From another approach, there are lots of ways to treat the surface of sculpture. Many of my sculptural pieces are intended for controlled environments (kept in the house or barn) and after the bisque firing, the pieces are rubbed with a thin coating of raw moist clay - different naturally colored clays provides a palette similar to earth-tone chalk used in drawings. Applied carefully, the surface does not flake. There are many 'dry glaze/stain' alternate approaches (relative to glazes, etc.) for sculptural ceramics. LT Thank you so much Magnolia. I will go ahead and do a few ‘test’ firings as you suggested. I believe now that I should have started by doing that. The enthusiasm of the novice. I will also fire again the sculptures with the marks and seee what comes out of it.....hopefully not all in pieces!! Many thanks!! Link to comment Share on other sites More sharing options...
AnaLucia Posted March 28, 2018 Author Report Share Posted March 28, 2018 54 minutes ago, Rae Reich said: Sometimes my bisque fired pieces have had "bleached" looking areas, but it was never a problem since I glazed them. I always assumed that it was caused by proximity to the heat source. Yes. I noticed that the areas near the heat were more affected. I am talking to The company that build my kiln and ask if this is the case. Will feed you back when I have a reply. Link to comment Share on other sites More sharing options...
AnaLucia Posted April 3, 2018 Author Report Share Posted April 3, 2018 UPDATE Thank you everyone for your comments on this post. I followed some of the advice and here is my results: 1 I washed some of the pieces with no change to the white marks. 2 I have fired again all my pieces to a higher temperature. Most of my pieces changed colour but (as the photo shows) they now look as if they have 'burns' in certain areas. 3 I will now follow Magnolia Mud Research (LD). I have made samples of the dieferent clays I have and will fire them in one go, to a higher temperature to see the results. I am learning and realised that all I want is to do just one fire as I don't intend to glaze or stain these pieces. Let me know your thoughts please, Best wishes! Link to comment Share on other sites More sharing options...
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