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Everything posted by SweetheartSister

  1. Oh, that makes sense! So put in the freezer for a day, take out and straight away pour over boiling water in the sink? Do you carry out this test with every single batch of mugs you fire, or just the once if you're duplicating the variables such as firing time/temp, layers of glaze used, same glaze and same clay etc?
  2. Oooh okay, that sound straight-forward enough to do. Is it important to make sure that you're testing with the exact item, e.g. using a cast out pendant to test rather than a different casting/piece of clay which is a different size? Like if I were to glaze a mug and a pendant in exactly the same way and fire them for the exact same schedule, would the results be different due to scale of the items? It makes the most sense for me to cast out some pendants as tests, but I'm just really curious as to what the variables are here
  3. Thank you Roberta12, Min and Neilestrick; it seems that the verdict is to try the overglaze on top of dry underglaze so that I don't have to fire 3 times. I'm going to do some test pieces and see how that goes. In the future I would definitely like to put a clear overglaze on some of these designs, but I am still fearful of crazing happening even a year down the line, which is what has happened on some of my earthenware pieces. Is there a fool-proof way to be sure that the glaze fit is definitely okay? I actually contacted a factory recently about batch producing some of these pendant designs in earthenware, but when I asked if they would eventually craze, they said definitely. I also spoke to my kiln supplier on the phone and he said that porcelain is a much safer option regarding crazing because it is a much less porous clay than earthenware. As I'm selling these, I just want to be sure that they will last a long time so that my customers are happy
  4. Thank you for this very detailed explanation, Min. I honestly appreciate it so much. I feel a bit stupid, firing the underglaze to vitrification temperature - I know that glazes don't take well on vitrified clay so I'm not sure why that completely went over my head. With regards to these pendants, they actually look really nice as they are without an overglaze, so for this batch I will leave them as is: 20190923_074045 by Rachel Brown, on Flickr If I wanted to repeat this process to accomodate a transparent overglaze in the future, do you think the following would work: 1. Bisque fire casts to Cone 05 2. Paint on underglaze and fire to cone 015 to burn off impurities 3. Paint on overglaze and fire to cone 7 (will mature at 6) to create final, vitrified piece. I don't think I could do liambesaw's suggestion of painting onto greenware, as the pieces are so fragile before bisque firing - it is very easy for example to chip off an ear on a pendant once dried. With regards to crazing, the supplier has recommended this exact overglaze to pair with the slip I am using from the same supplier. It is designed specifically for porcelain. So hopefully it will be okay, so long as I fire to the correct temperatures.
  5. I have a few dozen porcelain pendants in the kiln right now. This is my first time using porcelain and since having a bad experience with crazing on my last pendants (in earthenware) I really don't want to mess it up. This is what I've done so far - 1. Bisque fire to Cone 05 at medium speed. Although I have now discovered that if you don't put a hold on my electric kiln, it will shut off when it reaches each temperature and will not soak the ware at that temperature. So going by my pyrometric cones, they reached cone 06 (orton cone puddled) but did not quite bend my 05 cone. 2. Then I hand painted my pieces with Amaco Velvet underglazes and set the electric kiln to cone 7, firing at medium speed once again. This means it will definitely mature at cone 6. Firing range of the slip I'm using is 1220 - 1300 celcius. Cone 6 is 1220. I've put orton cones in again to be sure that the ware reaches cone 6 and therefore vitrifies. 3. The final stage will be to apply the transparent overglaze. This also has a firing range of 1220 - 1300. Should I fire at Cone 7 again? Should I fire on the fast setting or on the medium again? I have a Paragon Firefly kiln and according to the manual the medium speed is 'standard', the fast speed is 20% faster and the slow is 20% slower. I want to make sure I get these right this time, but feel quite nervous. These porcelain pendants will be used as part of fine jewellery pieces and I want them to last many many years and not craze on the surface. Thanks so much everyone.
  6. Thanks Bill and Liam for the advice. I'm going to experiment with it and will let you know if it is successful
  7. Just a little thought I had today...if I wanted Cone 6 fired porcelain to have a satin/low gloss finish without the use of an overglaze, do you think that I could achieve this using a rock polisher? I'm talking about very small items - pendants and beads. I would be interested to know if anyone on here has ever tried putting porcelain in a rock tumbler machine before?
  8. Hi Min, thank you for that suggestion because I would have never thought of that. If the method I'm trying today doesn't work out then I will certainly give that a go!
  9. The problem is that I can't really dry foot them. They need to be glazed all over. They are very small, 1cm -2.5cm each. Surely there must be ways to stilt or suspend porcelain that needs to be glazed all over, such as dolls? These are the pendants (pre-bisque fire) They have holes in the heads where the pendant bails will go - they could slot onto wire uprights on these. 2019-09-14_12-59-59 by Rachel Brown, on Flickr
  10. That is good to know Bill, thank you! I'll give the alumina and wax a try
  11. Thank you for your helpful response. I do have a homemade bead rack which I've used with success in the past, but with the case of these pendants, the holes do not go the whole way through the sculpture, meaning that they can't be threaded onto a bar. So the only way to suspend them is by slotting them onto an upright piece of wire stuck into a clay slab. It has worked for me many times with earthenware, but this is my first time using porcelain. I'm hoping that as the pendants are so very tiny, they won't slip down onto the sticks and get stuck. They are very light weight. I guess I won't know until I try.
  12. This might be a silly question, but I remember reading somewhere that porcelain cannot be stilted because it becomes very soft during firing and will slip onto the metal wires. Is this true? I have a collection of small porcelain pendants to fire, ranging from 1cm - 2.5cm. I was planning on bisque firing them on a shelf with kiln wash to 1000 celcius. After underglazing, I was going to suspend them on a homemade stand which is basically a slab of clay with nichrome wire sticking out of it. Each pendant has a hole in it so it can be suspended without the underglaze/overglaze touching anything. This is what I have done successfully in the past with earthenware, but will it work with porcelain? I'm aware that I will need to make a new stand in porcelain which will be okay during high fire. Many thanks in advance for your advice
  13. Does anyone know of any companies, preferably in the UK or Europe, who will batch manufacture porcelain for designers? I've found a few places in the UK who will do so in earthenware, but not porcelain. Any leads would be super appreciated! Looking to just get pieces cast/bisqued ready for hand painting.
  14. I've been advised that earthenware will always craze eventually, because it always remains slightly porous. Is this true? I've been advised that porcelain is a better bet for product longevity. I make and sell ceramic jewellery. Have been using earthenware up until now but am considering porcelain. The only thing is I've heard it takes a lot longer to slip cast. Would love some opinions on this from the experts on this forum
  15. Both I guess - I want to know if they are particularly dangerous for me to use, and also if they would be any danger to the wearer of say a pendant decorated in china paints. I have used Amaco underglazes on my earthenware jewellery in the the past, so maybe I could try these again on porcelain, although I'm away that the colours would change at high firing temperatures.
  16. So I'm quite new to ceramics (I started self-teaching back in November) and I really want to feel more confident on the technical side of things - that is how to get a perfect COE fit, the whens and whys of firing, maybe even glaze recipes if that's the only way to know for sure if your glaze will fit your clay body nicely. Can anyone recommend any books, videos, articles etc which give good explanations, advice and tutorials for someone working at my level as more of a beginner? I mainly make jewellery, but have been working on dolls too. I was a professional sculptor in the film industry prior to going freelance, so I am very confident with sculpting, mould making and casting. It's the ceramic-specific things which I need to understand better. I have been working with earthenware, but want to start using porcelain instead. Any advice is much appreciated, thank you!
  17. Has anyone on here used china paints on porcelain before? The popular brands are Willoughby's and Seeley's. They have a lovely, wide range of colours, but I'm concerned about the toxicity. If anyone on here has worked with them before, I would be interested to know how you have done so safely. If not, are there other ways of decorating porcelain with multiple colours and lots of detail?
  18. Hi Douglas, thank you for this very informative response. So from what you are saying, I now understand that glaze and body 'fit' being mismatched is what causes crazing, and this can happen even if clay body/glaze are within the same firing range, because it's all down to the chemical composition of both clay and glaze, and if these two are not aligned then crazing or shivering can occur? I don't feel like I'm at the stage yet where I can try making my own glazes, so this is what I'm thinking I should do to see if the fit is good: 1. Contact manufacturer of the slip I use and find out which clear overglaze they recommend as being the best fit 2. Bisque & overglaze fire test pieces to recommended schedule, using Orton cones to track/record heatwork 3. Stress test by putting in freezer and then in boiling water, repeat. Use ink to check for hairline crazing. 4. If this first attempt fails, repeat until I find the 'sweet spot'. Something I would like to confirm - you said 'Just because your glaze and clay are firing to the same cone, does not mean the glaze will fit the clay. ' But can crazing also occur if the clay body has been fired to the wrong temperature, even if the glaze and clay body would be a good fit if fired to the correct maturity? The reason I ask this is that I re-fired the pieces mentioned in my original post to a higher temperature, and the crazing has completely gone. Several days have passed and they are still okay. I believe those pieces crazed because I under-fired the clay body. However, I imagine the thermal shock test is the best way to know for sure if you have a good match with commercial clay bodies/glazes? It's very important to me that I get to the bottom of this so that I can sell my work with confidence in the future. I'm overflowing with creativity right now, but I need my technical skill and knowhow to be up to scratch! Thanks so much for your help.
  19. Lovely work! I'd be interested to know which underglazes your wife uses on her porcelain?
  20. I suppose that doing test firings is the best way to hit that sweet spot, as you say. I've been reading that freezing and then pouring boiling water over a finished, glazed piece is the best way to see if it's a good fit on or/will be long lasting. So I think I will try that with each batch of tests, until I don't get crazing anymore. Something else I read though, is that earthenware always remains a bit porous, and therewill be inevitably craze at some point in time? If this is the case, would it be advisable for me to try porcelain instead in the future? I have been reading that porcelain has a very high density, and due to it being a high fire ceramic, it is less likely to craze over time (so long as the clay and glaze are a good fit, etc) I really hope I can crack this! The enjoyment for me is in the designing, sculpting and making, but obviously getting the kiln temps and timings right is so important in creating a chemically stable, beautiful piece.
  21. Thanks so much for your response Bill, this is extremely informative. I think what has thrown me off and muddled me is that my earthenware casting slip and my clear overglaze both have wide firing ranges. My earthenware slip's recommended firing temp is 1080 - 1140 celcius. Which is Cone 03 - Cone 2. So how can I know which cone is the best to fire to, or is this suggesting that the kiln will reach maturity within this range? Similarly, my transparent glaze has a firing range of 1000 - 1140 celcius. In the past I fired the bisque to cone 01 and the transparent glaze to 05 and this worked for me, however, when I included some larger items in the kiln, that is when crazing occured. So I wonder if the 'fit' was not good enough with this combination, and it needs adjusting. How can I know that a glaze and clay body will fit each other well? Particularly as I am using commercial/ready made slip and glazes. Sorry if these questions have obvious answers - I have been doing a lot of research but still don't feel like I understand entirely.
  22. Hi everyone, I want to do some test firings to make sure that my jewellery pieces are reaching maturity (I have been experiencing some crazing issues). Both my slip and overglaze have a wide firing range across three cones, so I was planning on using three orton cones in each firing to see which cone is the optimum temperature to fire at. My work is really tiny - some of the pieces are less than 1cm x 1cm. Should I test fire using actual jewellery pieces, rather than test tiles? Because the tiles would be much bigger, and the rate that they mature won't necessarily represent the rate at which the tiny pendants mature? I really appreciate any advice or insight on this matter, thank you!
  23. Thank you for this, it's extremely informative. The way that I thought the hold worked was to make sure that the temperature stayed on the desired cone for long enough for it to have an affect, if that makes sense. I didn't realise that it goes up a cone by roughly 20 minutes at a time, which just goes to show how little I know - I will glady admit that I am very uneducated about ceramics and have a lot to learn. I've been doing a lot of research all day to try and fully understand why this might have happened, and if we can go back to absolute basics for a second, how can we know how to get a good 'fit' with bisque and glazes? The earthenware slip I'm using has a firing range of 1080 - 1140 C, the Amaco Underglazes can be fired between cone 05 and cone 10, and finally the transparent gloss overglaze I have been using has a firing range of 1000-1140°C . Given that these ranges cover up to three different cones each, how do I know which cone is best for each firing? From my understanding, the bisque firing must always be a higher temperature than the undeglaze and overglaze firing, is that correct? So how much of a difference would it make if I fired the bisque on cone 01, 02 or 03? Or is it simply a matter of making test pieces, trying out different combinations and seeing which renders the desired result? I have been reading that crazing can still happen months later if the clay body and glaze are not a good 'fit' for each other. So I suppose I'm trying to work out how I achieve that perfect fit in my firings in the future? Finally, I think I may have worked out what when wrong with these particular pieces. My guess is that the bisque was not fired high enough, and that when it was removed from the kiln and began absorbing moisture from the air, the clay expanded and put pressure on the glaze. I guess this because crazing has never happened with pieces that I fired on cone 01 in the past. Also, if the firing temp of my clay slip is 1080°C-1140°C, am I right that 1080 is cone 03, and therefore cone 04 would not make the clay hard enough? It seems in general that bisque is fired between 04 and 06, which is why I got very confused. My friend recommended that I fire to cone 04 to avoid crazing, but it seems that with the materials I was using it really didn't work. Furthermore, in the Q&A section for this overglaze on Scarva, there are lots of people having problems with this glaze crazing on Earthenware. Scarva's response is 'Earthenware glazes are prone to crazing due to not fitting the clay body. Sometimes it is possible to do a high bisque and low glaze but then it can be difficult to get the glaze to fit the clay body. For functional pieces it is much easier to choose a stoneware clay body and stoneware glazes then it is possible to do a normal bisque to 1000oC and high glaze. Hope this helps.' This is a really good idea, I will definitely try this with one of the pieces. The overglaze says it will fire up to cone 01, so it might work. The only problem is that some of the underglaze colours might burn out a bit.
  24. Please can you elaborate? As I said I am relatively new to all of this. I wasn't having problems on cone 01 with 45 minute hold. I still have pieces which I made in November of last year using those temps, and they don't have any crazing.
  25. I don't know if this is also useful information to help figure out the problem, but I noticed when I drilled the holes in the pendants of this batch, the bisque felt softer than usual. I actually had an old pendant to compare it to which was much harder to drill. So is there a chance that at Cone 04/1060 C. the bisque was still too soft? Like I said, in the past I was firing the bisque to cone 01/1137 C. In the past I have not used orton cones, because there's no way I can see into the kiln. I'm wondering if I should try putting them in for a test firing and see what happens.
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