Jump to content

SweetheartSister

Members
  • Content Count

    12
  • Joined

  • Last visited

About SweetheartSister

  • Rank
    Member

Recent Profile Visitors

The recent visitors block is disabled and is not being shown to other users.

  1. 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.
  2. 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!
  3. 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?
  4. 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.
  5. Lovely work! I'd be interested to know which underglazes your wife uses on her porcelain?
  6. 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.
  7. 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.
  8. 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!
  9. 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.
  10. 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.
  11. 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.
  12. Hi everyone, I'm quite new to the world of ceramics. I purchased my kiln in November of last year and have been teaching myself everything using online resources, the instruction manual of my Paragon Firefly kiln, and have also been getting advice from a friend who has been a full time ceramics artist for several years now. I mostly make small items - jewellery and miniature dolls. When I started out, I had no problem with crazing. I was using white earthenware slip from scarva (recommended fire temp 1080°C-1140°C), Amaco Velvet Underglazes (recommended fire temp 1040°C - 1220°C) and Scarva GZ2108 Transparent Earthenware Overglaze ( recommended fire temp 1000-1140°C) The first items I made back in November were Christmas ornaments, which were a reasonable size, about 8cm tall. I fired the bisque on cone 01, on medium speed with a 45 minute hold. I fired the underglaze on cone 05, on a fast speed, with a 45 minute hold. The overglaze was also fired on the 'fast' setting with a 45 minute hold. I had no problems with crazing, even though I was using three coats of the overglaze. Everything came out fine, and I continued to makes lots of mini pendants and brooches using these settings up until recently. What happened was that I designed a planter, fired it all on the same settings, and this is when I first experienced crazing. I told my ceramicist friend about what happened, and she suggested that I fired the bisque on cone 04 instead of cone 01. She also recommended that I don't do the hold at the end, as it was unnecessary and a waste of electricity/time. So I made a new planter and bisque fired it on cone 04, followed by the glazes on cone 05. The planter came out fine, so I decided that I would do the same for my next collection of pieces. Today I removed 6 weeks worth of work from the kiln. Everything looked fine and I has relieved. Then, about 3 hours later, I heard pinging. I was horrified to see the pieces all covered in crazing cracks. I have never, ever had any issues with crazing on my tiny pieces before, not with the firing schedule I used to follow. I decided to fire using the temps my friend recommended me to because I had a planter in this kiln load as well as the tiny pendants. I wonder if I opened the kiln too soon - I opened it at 90 degrees celcius. In the past I have opened it at around 150 degrees, with no crazing issues whatsoever. That's back when I was firing the bisque to cone 01. If anyone can advise me as to what I am doing wrong, or point me in the direction of some educational resources to help, I would really really really appreciate it. I'm going to assume that crazing cannot be fixed be re-firing? I'm sorry if I sound stupid - I am very new to all of this and am trying so hard.
×
×
  • Create New...

Important Information

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