Frank_G Posted June 15, 2016 Report Share Posted June 15, 2016 Dear Ceramic Arts Community, this is my first post - I am a ceramic enthusiast from Austria, hello everyone! :-) I am experimenting with Majolica decoration and I am facing a problem - please help me out. I glazed earthenware test tiles with a white glossy glaze and decorated it with colors in the majolica method. After the firing the colored areas all have some kind of texture, they are grainy - I don't know the exact term for this problem (variegated? mottled? speckled?). Here's a close up picture: I would like the colored areas to be as uniform as possible. How could I get a better result and why does this happen? Details Clay: white earthenware tile, bisque fired, I also tried red bisque fired tiles Glaze: white glossy glaze, applied by pouring, firing temperature 950°C-1000°C, I tried different white glazes and I am having the same problem Glaze composition: Na2O, K2O, CaO, PbO, ZnO, Al2O3, B2O3, SiO2, TiO2, ZrO2 Color: I tried Duncan Concepts, cobalt oxide, other decoration colors, I thought the particle size might be too big so I tried making them smaller in a mortar - no difference, I also tried thicker application and it's not getting better Firing cycle: electric kiln, oxidation, 3 hours to 600°C, another 3 hours to 990°C, holding time 15 minutes, cooling down without delay Thank you very much for your help, Frank Link to comment Share on other sites More sharing options...
Denice Posted June 15, 2016 Report Share Posted June 15, 2016 What do you fire your bisque to? I have a lot of problems with the overglaze if I the bisque still has organics in it. I use a majolica glaze and Duncan Concepts fire at Cone 1. Denice Link to comment Share on other sites More sharing options...
Marcia Selsor Posted June 15, 2016 Report Share Posted June 15, 2016 what are you using for a flux mixed in with the color? What are you using for color. The best information source for majolica that I know is Linda Arbuckle's website. http://www.readbag.com/lindaarbuckle-handouts-majolica-handout2007 Marcia Link to comment Share on other sites More sharing options...
Min Posted June 15, 2016 Report Share Posted June 15, 2016 My guess is that it would be from the TiO2 in your glaze causing the mottled effect. Not trying to be a nag but is the lead really necessary? Link to comment Share on other sites More sharing options...
Babs Posted June 15, 2016 Report Share Posted June 15, 2016 Are all your colours doing this or just the cobalt oxide, I find Cobalt Carb. more prone to speckling than the oxide.? I mix the colours as Marcia says with a frit to flux or Gerst. borate for same reason. 990dC is what cone? cone 06,..07? Is the glaze mature at this temp and the only prob. areas are where you apply colour? I know I really stir the onglaze colours all the time ie between brush loads. Mottling may be when you use the oxide as opposed to a premixed colour. texture may be that as Marcia says you need to flux the colourant. Ot it's way too thick. Link to comment Share on other sites More sharing options...
Marcia Selsor Posted June 16, 2016 Report Share Posted June 16, 2016 The recipes I have used fire to ^03, 2014 F or 1104 C. The pasted info below is from Arbuckle's 2007 handout Majolica and Lowfire Information Majolica (Arbuckle) Cone 03 Cone 05 + ½ - 3+ tbsp. Epsom salts. to 5 gallons of glaze (flocculates the glaze for less settling and better application). Smooth, white, opaque. Colorants w/flux usually applied in a thin wash to raw glaze surface. Does not move in firing. May crawl if thick in corners or pinhole over rough-trimmed surfaces. Fire w/small 03 cone in the sitter to give a small 04 tipped to about 2 o'clock in front of the peep hole. Use of chrome in decoration may cause sufficient fuming to make the background blush pink in high tin glazes (above 5%). If this is a problem, drop the tin a bit, and add that amount x 1.5 of additional zirconium opacifier. frit 3124 65.8 66.6 F-4 feldspar 17.2 23.0 EPK 10.8 2.3 neph sy 6.2 8.1 100.0 100.0 + tin 4 4 + zircopax 9 9 + bentonite 2 2 Majolica Colorant Suggestions: Gerstley borate is no longer being mined, and was erratic in quality when it was. It made color pastel through very fine reticulation (break up) on the surface, and although I used GB when I began majolica, I now use frit as a flux (with bentonite added) or commercial majolica decorating colors. Colorants with just frit settle quickly, have limited brushability, and are very powdery dry. Some artists, like Matthias Ostermann, use this quality to work the surface like pastels. My methods resist the motifs with wax before a solid ground color is laid in, and the addition of bentonite or use of CMC gum to the frit + colorant mix aid brushing and hardens the dry surface. Bentonite doesn’t mix easily w/water, so be SURE to mix dry bentonite, frit, and colorant first, then add water. I use frit 3124. Others will work, with color reactions influenced by frit chemistry. To aid brushability, you may add a small amount of glycerin (drug store item), or a few drops liquid CMC gum to the liquid mix. For things that melt easily at low-fire temps (copper, cobalt, iron) try 1 part colorant, 1 frit, 1 bentonite by volume. For more refractory ingredients, test 1 colorant, 2 frit, 1 bentonite. 1 part colorant, 1 frit, ½ - 1 bentonite 1 colorant, 2-3 frit, ½ - 1 bentonite Copper (blue-green), cobalt (blue), manganese (brown to plum w/3110), iron (brown) Chrome (grass green), rutile (rusty orange), titanium (ivory), most stains Note that stains intended as “body†stains – to color clay bodies – are too refractory, even w/flux added, to make a smooth surface on top of majolica glaze. Some of those stains: Mason 6020 Manganese-alumina pink, Mason 6485 Titanium yellow, one of the lavender Mason stains. I find that Vivid Blue is also rather refractory. Some AMACO Velvet underglazes work for decorating on top of majolica base glaze: Mist Grey, Jet Black, Rose, Maroon, Leaf Green and 350 Orange, Amethyst, Violet, Real Orange, Lt. Red, Red. Too refractory to use: Electric Blue, Pearl Grey, Ivory, Hunter Green, Deep Yellow, Straw, Lt. & Med. Pink . Test others. AMACO now makes a series of colors specifically for majolica decoration, the GDC series of products. Good range of 36 colors. They work well right from the bottle for decoration on top of the base glaze. Prices for small jars are $3.50-5.75, pints $12 -38.00. The colors will inter-mix, but as with the colorants they are made from, some are strong colors, others weaker, so you may need to test amounts. E.g. 3-4 parts Yellow and ½ - 1 part turquoise makes a nice chartreuse. Linda Arbuckle Majolica and Lowfire Information http://lindaarbuckle.com Page 2 of 10 Soluble colorants: cobalt sulfate (blue), copper sulfate (turquoise), manganese chloride (plummy brown), chrome chloride (green). All are toxic raw. Do not inhale, ingest. They are also absorption hazards: do not handle these w/o gloves. Soluble colorants are dissolved, rather than suspended in water, so they wick with the water making a very uniform ground color and leave a soft edge,. If you want a white areas, or to retain motif colors, areas must be waxed before applying soluble colorants. Over-wetting the glaze when applying solubles may move raw glaze and cause color to migrate thru the pot wall and/or crawling. Too much water on the raw glaze may cause crawling in the fired glaze. Majolica Link to comment Share on other sites More sharing options...
Babs Posted June 16, 2016 Report Share Posted June 16, 2016 Such great info, thanks Marcia Link to comment Share on other sites More sharing options...
Frank_G Posted June 16, 2016 Author Report Share Posted June 16, 2016 Wow, thanks for the help and all the replys. @Denice: I also thought that the organic material might be a problem. I bought some bisque fired tiles and don't know the exact temperature they have been fired to. But I also bisqued tiles myself to 950°C (Cone 08). @Marcia: The Duncan colors are liquid so I used them as they are. I mixed the cobalt oxide with a little transparent glaze and water. The decoration/overglaze colors (powder, not as strong) were also mixed with water. I will try again with the Arbuckle white Majolica glaze and colorant+frit+bentonite. @Min: I will try the Arbuckle Majolica glaze (without TiO2 and lead) and post the results - hopefully tomorrow. @Babs: It happened with all of the tested colors - cobalt oxide, Duncan concepts and decoration/overglaze color. Sorry, 990°C is approx. cone 07, 1814° Fahrenheit. The white glaze is nice and everything is flat and shiny. Maybe there is mottling in the white glaze, but in the colored areas it can be seen. I will try to post the result of my test tomorrow Edit: I just saw that when I hold the tile against the light the white glaze surface doesn't seem to be completely flat, there are tiny bumps. Does the rough structure of the earthenware tile have something to do with this? Link to comment Share on other sites More sharing options...
Babs Posted June 16, 2016 Report Share Posted June 16, 2016 Sieve and test unsieved and sieved glaze Link to comment Share on other sites More sharing options...
Frank_G Posted June 20, 2016 Author Report Share Posted June 20, 2016 Sorry for the delay, I let the glaze dry for one day and the firing took another day. I did a test with Arbuckle's Cone 05 Majolica Recipe. But as some of the ingredients are hard to get in Europe I had to change a few. I used Kaolin instead of EPK and Feldspar (half Kali Feldspar and half Natron Maxum) instead of Minispar 200. Sadly, it made no difference. The drawing has the same texture as in the upper picture. This is what I did: I measured the glaze ingredients, added water and stirred them thoroughly. Then I sieved the glaze with a 80 mesh sieve and a 100 mesh sieve. After that I poured the glaze over the test tiles and let them dry for a few hours. Then I painted onto the tiles (color, frit 3124 + bentonite mixed thoroughly) and let them dry until the next day. They were put into the electric kiln at Cone 05 (3,5 hr to 600°C, 3 hr to 1050°C, 12 min holding time, cooling down normally). This time I let the ventilation slider on the bottom of the kiln open through the whole firing process, because I thought it might help burning out gasses or something like that. The glaze turned out white and pretty glossy, but the drawing has the same texture as in the upper picture. The white glaze itself has a strong texture (looks "pixelated") and I think in the colored areas it's just more obvious. It's hard to photograph, but I hope you can see it in the pictures. Holding the tile against the light you will see a bumpy surface. I sanded the surface of one bisqued tile really smooth but it also happened there. I am really trying to solve this issue and would really appreciate further tips. Thank you. Here are two pictures of the white glaze: Link to comment Share on other sites More sharing options...
Babs Posted June 20, 2016 Report Share Posted June 20, 2016 Cant see this really but test mixing the colours with the glaze you're using just do a test tile. Some colourants may need more glaze than others. Some say to slake the glaze before sieving etc, A matter of testing. This all seems so simple on paper! I've even layered a thin glaze cover over some obstinate colours but you have to use the base glaze prior to adding tin, and zircon pax...life shouldn't be so hard, eh? Test at C03 could need a higher temp One at a time for changes they say.... Link to comment Share on other sites More sharing options...
Marcia Selsor Posted June 21, 2016 Report Share Posted June 21, 2016 MIn and Frank, Why are you adding titanium to the majolica? it calls for tin or zircopax. Where did your info on composition of glaze come from and why are there no percentages? Glaze composition: Na2O, K2O, CaO, PbO, ZnO, Al2O3, B2O3, SiO2, TiO2, ZrO2? SNO2 is tin oxide TIO2 is titanium marcia Link to comment Share on other sites More sharing options...
Marcia Selsor Posted June 21, 2016 Report Share Posted June 21, 2016 I agree. And also the recipes with percentages not just ingredients. it makes me wonder because Frank doesn't mention titanium just the chemical symbol. could he be confusing it for the symbol of tin? I see people write RIO all the time for red iron oxide. It would help greatly to see what the % are for the recipe. marcia Link to comment Share on other sites More sharing options...
Marcia Selsor Posted June 21, 2016 Report Share Posted June 21, 2016 I took a very close look at the pixelation of the white glaze. I suggest using water with vinegar added to dip and wash your bisque before glazing. After glazing, smooth any blemish with a dry finger. You can use hair spray to stiffen the glaze and then paint THIN coloring decoration over it. I my experience and with others I worked with in a coop, we'd bisque to ^ 02 or 03 and glaze fire to 04, This reduce crazing which had been a problem on the terra cotta we were using. marcia Link to comment Share on other sites More sharing options...
Babs Posted June 21, 2016 Report Share Posted June 21, 2016 Frank says he uses Arbuckles 05 maj. glaze in his later psot where he is still suffering the same prob i.e. colours not merging with the underlying glaze. I agree Marcia the colorants may be being used in a too thick state, or not being stirred whereby the frit may be settling out prior to being applied. Link to comment Share on other sites More sharing options...
Marcia Selsor Posted June 21, 2016 Report Share Posted June 21, 2016 I think also the glaze is going on too thick if you take a close look at what he calls the pixelated surface. BY washing the bisque in water with vinegar, it will slow the absorption rate and clean the surface. and I agree the decorative color ants are on too thick. BIsque firing higher than the glaze helps too. Marcia Link to comment Share on other sites More sharing options...
Frank_G Posted June 21, 2016 Author Report Share Posted June 21, 2016 Where did your info on composition of glaze come from and why are there no percentages? Glaze composition: Na2O, K2O, CaO, PbO, ZnO, Al2O3, B2O3, SiO2, TiO2, ZrO2? SNO2 is tin oxide TIO2 is titanium The first glaze I mentioned was a commercial glaze, so I don't have the exact percentages. Here is the info from the manufacturer: 40-80% SiO2, 20-40% PbO, 5-10% Al2O3, 5-10% ZrO2, 1-5% B2O3, 0,5-1% CaO, 0-0,5% TiO2 (it's just a little titanium, there's no tin in this glaze) But I had the same problem with Arbuckles Majolica Glaze (66,6 % Frit 3124, 23% feldspar, 2,3% kaolin, 8,1% Nepheline syenite, 4% tin, 9% zircopax, 2% bentonite - with a few changes mentioned above). I took a very close look at the pixelation of the white glaze. I suggest using water with vinegar added to dip and wash your bisque before glazing. After glazing, smooth any blemish with a dry finger. You can use hair spray to stiffen the glaze and then paint THIN coloring decoration over it. I my experience and with others I worked with in a coop, we'd bisque to ^02 or 03 and glaze fire to 04, This reduce crazing which had been a problem on the terra cotta we were using. marcia Thank you for assisting me and I will try the dipping before glazing. I have some pieces with very thin white glaze (too thin, you can see through) and they also have this strange mottling. There I thought it's because it's too thin and the tile's texture shows through. I also tried thick and thin decoration I agree Marcia the colorants may be being used in a too thick state, or not being stirred whereby the frit may be settling out prior to being applied. I ordered a hand blender and will stir it wildly to make sure the glaze and color is mixed well. As it happens with multiple glazes and multiple colors it really seems like I am doing something wrong in the glazing/decoration process. Link to comment Share on other sites More sharing options...
Babs Posted June 21, 2016 Report Share Posted June 21, 2016 I'd take it higher to C03 Frank and let it soak there, just a test to see if the colourants will melt into your glaze. How many degrees are you going up in the final hour? May need heat work to get the melt. I say this as you are experiencing this with lots of colours. I've only had it with a couple which contained clay...I use underglazes on top of majolica and only a blue doesn't get there. Link to comment Share on other sites More sharing options...
Frank_G Posted June 21, 2016 Author Report Share Posted June 21, 2016 I'd take it higher to C03 Frank and let it soak there, just a test to see if the colourants will melt into your glaze. How many degrees are you going up in the final hour? May need heat work to get the melt. I say this as you are experiencing this with lots of colours. I've only had it with a couple which contained clay...I use underglazes on top of majolica and only a blue doesn't get there. Don't you think that the colorants melted properly? The areas are shiny and in the majolica glaze the colored areas have even sunk a little into the glaze (they are a little lower). I go from 600°C to 1050°C in 3 hours with about 15 minutes soaking time, at the moment I don't know how long the last hour takes. With "lots of colours" I meant different kinds of blue colorants (Duncan concepts, cobalt oxide, decoration color). There's one more thing I have to mention and it might sound strange: I bought a standard white glazed tile at the hardware store and brushed colorants onto the fired glaze with a little medium and fired it to 1050°C. The result has no such texture, but the white glaze lost a bit of its gloss. Of course I have no idea to which temperature this white tile has been fired to originally. Here's a better picture of my decoration problem (here it's cobalt+bentonite+frit 3124+water on the mentioned Arbuckle Majolica glaze). I hope it's not getting too complicated now and I'm not annoying. Thank you! Link to comment Share on other sites More sharing options...
Marcia Selsor Posted June 21, 2016 Report Share Posted June 21, 2016 I bought a tile and used it as a color chart. The colorants came out very well just as your s did. They were ones I mixed. Try adding some glycerin to your colorant mix. It may help with flow. I would also fire hotter like Babs suggested. 20-40% is a lot of lead. Traditional majolica did have lead. Hopefully the source in your glaze is fritted. I would stay away from raw lead. Good luck and let us know if you get some success. Marcia Link to comment Share on other sites More sharing options...
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