Elaine Posted October 30, 2010 Report Share Posted October 30, 2010 Hi everyone. I spent 7 years in England hand painting ceramic white glazed tiles using 'on glaze'. Since emigrating to Australia I thought I would set up a studio and get back into painting again. But I have a problem. I cannot fire the black, cobalt blue or iron red without them severly cracking. Sometimes the paint peels off the tile as it is drying on the tile and hasn't even touched the kiln yet. Other times they are fine, go in the electric kiln and come out cracked up. All other colours, I have 30 of them fire beautifully. Even on the same tile, the other colours fire great but the black/blue/iron red cracks. Things I have tried: Leaving the tiles out for 24 hrs to dry before putting them in the kiln - result: no difference. Slowing the firing down - 25 deg per hour up to 150 deg, hold for 20 mins, then fire up to 797 deg at 100 deg per hour - result no difference to the faster firing. Doing 10 test strips with the black on 2 tiles, mixing the black with various different fluxes/soda feldspar/ - result: they all came out perfect - even the dummy one that I added nothing too! Painted some tiles with the new mix, result: cracked. Why were the tests perfect when the firing I did was no different to what I normally do when they crack? Fired with all flues closed - result: cracked. Fired with top flue open - result: cracked. Bought the same brand of on glaze that I used in England with no problems for 7 years - result: blue and black cracked. Left bigger gap in between tiles whilst firing - result: cracked still. Could it be the water based medium? It is different to the one I used in England. If so, why isn't it affecting the other 30 colours I have? Could it be something that is in those 3 colours that is reacting with the white glaze on the tiles? The firing temp of these paints says on the side 800 deg. I fire to 797 deg for all colours except red and orange where I fire to 794 deg. I get fantastic colours. Last night whilst firing what turned out to be my latest batch of failures, I happened to check the kiln as it reached it's peak temperature. I hold it there for half an hour. But I noticed the kiln was over firing to 802 deg. Could this be why? The cracks are severe, almost like they are evaporating with collective blobs. Is that over firing????? If so why aren't the other colours doing the same? Will cooling down too quickly affect the paint? It took me a long time to find the right glazed white tiles. I know on glaze means that the paint sits on top of the glaze but in England I used specific tiles where the paint sank into the glaze so when you ran your hand over it, it felt smooth. I have just found a tile that can do that here so I am reluctant to swap tiles. Some feed back would be much appreciated as I am now at a loss on what to do! I don't understand it!!! Link to comment Share on other sites More sharing options...
Chris Campbell Posted October 30, 2010 Report Share Posted October 30, 2010 I cannot help with the chemistry part, but maybe it would help to discover what parts of your process have changed from how you did it in England. Did you buy another kiln or did you transport it? Is the power source the same? Are the tiles the same clay body? Is the glaze the same formula? Do you make the glaze from raw ingredients or do you buy it pre made? Are all the over glaze type products the same? It is pretty amazing how one little variance can cascade. Link to comment Share on other sites More sharing options...
Elaine Posted October 30, 2010 Author Report Share Posted October 30, 2010 I cannot help with the chemistry part, but maybe it would help to discover what parts of your process have changed from how you did it in England. Did you buy another kiln or did you transport it? Is the power source the same? Are the tiles the same clay body? Is the glaze the same formula? Do you make the glaze from raw ingredients or do you buy it pre made? Are all the over glaze type products the same? It is pretty amazing how one little variance can cascade. Yes the kiln is a new one, different from England - both electric though. Kilns are like people - they all have different personalities/characters. But a different kiln doesn't solve the problem of why 27 colours are firing beautifully and 3 are cracking. My partner is an Electrician and says the power source is the same. I buy glazed white tiles ready for painting - the ones you get in tile shops so no I don't make the glaze myself or buy pre mixed. I would say the clay bodies would be different from Englands as would be the white glaze on them. I don't know what I had in England, just that they worked and fired the paint in beautifully. The tiles I have here fire in 27 of the colours beautifully. I bought on glaze from here Australia and I also bought the same on glaze I used in England - both are cracking on the black and blue. Thanks for showing an interest and trying to help. It helps talking to some one and thrashing through possibilities!n You are right in that it is probably one tiny small thing that is making a huge problem. Link to comment Share on other sites More sharing options...
Chris Campbell Posted October 30, 2010 Report Share Posted October 30, 2010 Well, now we have to call on the chemistry majors! HELP!!! I would look for a common denominator in the ingredients of the problem colorants. I think it is not fluxing with your glaze. Once you find the ingredient common to them all you might have a better idea how to fix it. I'm suspecting iron but I am no chemistry lover. Link to comment Share on other sites More sharing options...
Pres Posted October 30, 2010 Report Share Posted October 30, 2010 Well, now we have to call on the chemistry majors! HELP!!! I would look for a common denominator in the ingredients of the problem colorants. I think it is not fluxing with your glaze. Once you find the ingredient common to them all you might have a better idea how to fix it. I'm suspecting iron but I am no chemistry lover. Not a chemistry major here, but it sounds like to me your glazes are not fitting the clay body. In other words the shrinkage/expansion of the clay body is much different from that of the glazes so you have the shivering and the cracking problems. Link to comment Share on other sites More sharing options...
Les Posted October 30, 2010 Report Share Posted October 30, 2010 This may sound too simple, but instead of trying to figure out the glaze chemistry,etc. (endless work); just go out out and buy a different brand of the black, cobalt blue or iron red, and see what happens. For some reason, those colors may have a chemical in them that doesn't work well under your current conditions, so the most simple plan of attack is to try another brand. Link to comment Share on other sites More sharing options...
Elaine Posted October 31, 2010 Author Report Share Posted October 31, 2010 This may sound too simple, but instead of trying to figure out the glaze chemistry,etc. (endless work); just go out out and buy a different brand of the black, cobalt blue or iron red, and see what happens. For some reason, those colors may have a chemical in them that doesn't work well under your current conditions, so the most simple plan of attack is to try another brand. Ok, I will get onto this today. I already have another brand - I have Northcote Pottery here in Australia and I also bought Pottercrafts brand from England (the brand I used when in England). Tomorrow I am going out to source different tiles so will test both brands on different tiles in the same firing. I will also buy Pottercrafts water based medium and see if that makes any difference as it is very diffeent to the Northcote medium I am using. Unfortunately it will take a week to arrive from England, but in the mean time I will get on with testing both brands on different tiles. Will let you know results in a few days time. Thanks guys for the much needed support. Link to comment Share on other sites More sharing options...
Guest JBaymore Posted October 31, 2010 Report Share Posted October 31, 2010 I do overglaze enamels ("on glaze colors") so have a bit of experience with this stuff. The base glaze onto which you are firing the enamels (china paint) can have a big effect on the overglazes. It is possible that the new tiles you are purchasing have a diferent formulation of the basic white glaze that is on them. This could be affecting the particular colors. I've sen the base glaze greatly affect certain colors in weird ways. Try a different source of the white tiles. What would be BEST is if you could get some of the same tiles you were using in the UK and test on them. If they come out OK on those old tiles...... it is the new base glaze. best, ...................john Link to comment Share on other sites More sharing options...
jo4550 Posted October 31, 2010 Report Share Posted October 31, 2010 Hello Elaine I am having difficulty trying to visualize what you describe as "cracked up" and"cracking" in your description of the tiles. Would you be able to post an image of the problem in question? Johanna Link to comment Share on other sites More sharing options...
Elaine Posted November 1, 2010 Author Report Share Posted November 1, 2010 Hello Elaine I am having difficulty trying to visualize what you describe as "cracked up" and"cracking" in your description of the tiles. Would you be able to post an image of the problem in question? Johanna Johanna DeMaine http://johanna.demaine.org http://overglaze.info http://allthatissublime.com Hi Johanna/Everyone, Yesteday I had a massive break through. I sat down to do some random samples with both brands of paint that I have, when I suddenly had a brain wave. I have enclosed one photo. It won't let me do two photos at the same time so I have encosed another photo in my next post. But in this first photo you can see that i have 2 columns of tiles. Tiles that I have completely covered in the blue which fired beautifully and 3 tiles that I have painted a picture on using the same blue and they cracked. Why? Why is one fine and one not? Answer: because I mixed a fresh batch of paint for the tiles on the right but used paint that I had left over from the day before for the left hand tiles. the paint is only a day old but dries out, so I scrape it off the tile, add some medium and reuse it. Now see the photo on my next post..... Link to comment Share on other sites More sharing options...
Elaine Posted November 1, 2010 Author Report Share Posted November 1, 2010 Hello Elaine I am having difficulty trying to visualize what you describe as "cracked up" and"cracking" in your description of the tiles. Would you be able to post an image of the problem in question? Johanna Johanna DeMaine http://johanna.demaine.org http://overglaze.info http://allthatissublime.com Hi Johanna/Everyone, Yesteday I had a massive break through. I sat down to do some random samples with both brands of paint that I have, when I suddenly had a brain wave. I have enclosed one photo. It won't let me do two photos at the same time so I have encosed another photo in my next post. But in this first photo you can see that i have 2 columns of tiles. Tiles that I have completely covered in the blue which fired beautifully and 3 tiles that I have painted a picture on using the same blue and they cracked. Why? Why is one fine and one not? Answer: because I mixed a fresh batch of paint for the tiles on the right but used paint that I had left over from the day before for the left hand tiles. the paint is only a day old but dries out, so I scrape it off the tile, add some medium and reuse it. Now see the photo on my next post..... I can't get the phot on....I'm not good with computers. Anyway, all the fresh painted tests - both blue and black came out lovely using both brands. All the tests re using paint that had already been mixed and sat on my shelf for a few days - all cracked and blobbed. But the interesting thing was - I also tested reusing paint in other colours and they all came out beautiful. Iit is just the re using of the blue and black. I haven't solved the problem but at least i know what the problem is now! I thought perhaps too much medium in ratio to paint - but all the otherscolours are fine being re used. Could be the cling film/cling wrap that i cover the paint with - is it reacting with the paint? Anyway, I am a step closer to solving the problem. I'll keep trying to down load this picture of my test. Link to comment Share on other sites More sharing options...
Deb Evans Posted November 1, 2010 Report Share Posted November 1, 2010 You add tape water to your paints? try distilled. Tap water can be a big varaiable. Link to comment Share on other sites More sharing options...
Elaine Posted November 1, 2010 Author Report Share Posted November 1, 2010 You add tape water to your paints? try distilled. Tap water can be a big varaiable. No I don't use water, I use a water based medium specifically for on glaze. Link to comment Share on other sites More sharing options...
Guest JBaymore Posted November 2, 2010 Report Share Posted November 2, 2010 If they are in a dusty studio environment and left uncovered for a long period... the dust can cause changes. They are very sensitive. What are you storing them IN? best, ..............john Link to comment Share on other sites More sharing options...
Guest JBaymore Posted November 2, 2010 Report Share Posted November 2, 2010 Aha.... looking at the picture...... It seems that the places it is crawling is coordinated with the places the overglaze is thickest. The overall color on the right tiles is thinner. A lot of times with certain colors in order to get the color deeper / darker/ thicker, you have to build it up over multiple firings. best, ................john Link to comment Share on other sites More sharing options...
Elaine Posted November 3, 2010 Author Report Share Posted November 3, 2010 If they are in a dusty studio environment and left uncovered for a long period... the dust can cause changes. They are very sensitive. What are you storing them IN? best, ..............john They are mixed on tiles that I then cover with plastic cling wrap/cling film - depending which country we are in! So no dust can get in but I am wondering if they are sweating? Link to comment Share on other sites More sharing options...
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