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Thread: Silver clay disaster! Please help!

  1. #1
    Join Date
    Mar 2013
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    Default Silver clay disaster! Please help!

    I've been running a fingerprint jewellery business for about three years and although when I began I had some issues with the backs breaking off cufflinks, that was resolved and I've had no problems since then. Until recently that is! After making lots of cufflinks for Fathers' Day I had a few returns where the backs had broken off only in a different way from before. Rather than a clean break leaving a cufflink face that I could sand down and start again, this time small amounts of the silver from the back of the cufflink face had come away leaving a little pit. What was inside looked like unfired silver clay which suggested that the kiln had been underfiring. I spoke to the man at Prometheus and emailed the manufacturer in Turkey and was advised to recalibrate it and buy a new thermocouple which I did. Today I soldered a couple of cufflinks that I made since recalibrating and installing the new thermocouple. I gave them a good pull afterwards to make sure they were connected but again one of them broke and again taking away some of the silver. I was baffled and wondered if the cream coloured powdery looking interior that had been revealed really was unfired clay so I took a wire brush to it and after brushing it looked silver. So I'm really confused. At this point I don't feel I should take any more cufflink orders and considering they make up a substantial part of my sales I don't know if I can even carry on with the business unless I get to the bottom of this. If there are any experts out there or people who've had a similar experience I would be so grateful to hear from you! Many thanks

  2. #2
    Join Date
    Dec 2009
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    Central London
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    Without offence I would urge you to abandon fired clay articles for sale, because the result is difficult to predict.

    Once you have made your prototype, send it to a caster, who can make and cast multiples from it and return them with a degree of finish if required.

    Your life will be worth living again. Dennis

  3. #3
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    I don't think anyone on here can answer your question properly as not many of us use clay. All I can suggest is that you fire it for longer than you normally do. I know a lot of people use it for fingerprints and I've done a few in my time. I've never had the problem you've been having though. Do you burnish the clay before soldering on the back? PMC is quite porous and you need to harden it. You also need to use a lot more solder than you would for sterling silver as the clay soaks it up.

  4. #4
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    Mar 2013
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    Thank-you both for your replies. I've been making and selling silver clay pieces with fingerprints, handprints and footprints for three years without any problem until now so I can't help thinking it's a kiln issue because whatever methods I've been using have worked until now. I was advised to sand the back of the cufflink before soldering to ensure that it's smooth enough although had read about burnishing and wondered if that would be better. Still I'm not sure that explains why a small amount of silver has chipped away when the cufflink post has come off. I know silver is a relatively soft metal but surely it shouldn't break like that?

  5. #5
    Join Date
    Feb 2011
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    As Carole has said few of us work with pmc so can't explain the chipping as it doesn't behave like sterling or fine silver. On the couple of occasions I have used it and had to solder onto it it has needed burnished to harden the surface rather than sanded or it swallows huge amounts of solder. If it hasn't happened before then you are right it's probably a kiln issue because no silver doesn't chip.

  6. #6
    Join Date
    Dec 2009
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    London
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    I do work in silver metal clay and am able to produce consistent results with the things I make, which are mostly rings and earrings. Sadly, we don't get to see/hear about the many amazing jewellery artists out there with skills creating amazing/beautiful and long-lasting stuff with this medium (e.g. Gorden Uyehara, Liz Hall, Celie Fago, Lisa Barth, Holly Gage)

    I'm sorry to hear about your current troubles with your cufflinks. As previous folks have said, it could possibly be that your kiln is not reaching a high enough temperature for sintering to occur. You don’t mention how long you fire your silver metal pieces for. If the firing time is too short (also known as ‘short-firing’) then problems can result in the final product. Work hardening your pieces afterwards with a hammer is also important - this is because when the metal comes out of the kiln, its fully annealed and therefore soft. The work hardening if done gently can be done safely without compromising any designs on the piece, before polishing.

    For example, those firing schedules listed in the packets of PMC3, are only minimum times and temperatures. A full firing at 1650 deg F (around 900 deg C) for 2 hours results in a much stronger material.

    A really useful guide to firing silver clay can be found on the cooltools.us website here. It contains lots of information about why a full 1650 F/2 hr firing of silver clay is important.

    It is possible to produce consistent results with silver metal clay and it certainly helps to understand the material that you’re dealing with and what is happening to it at a molecular level during firing. I always point folks in the direction of Kate McKinnon’s book ‘Sculptural Metal Clay Jewelry: Techniques and Explorations’. Kate McKinnon is a jewellery artist and scientist who when asked to test silver metal clay when it was first produced got together with her scientific chums to analyse this material under varying firing conditions and different processes to see what was going on with this material at a molecular level and to figure out what were the optimum firing conditions to produce a strong final product.


    Hoping you find a solution to your current issues.

  7. #7
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    Apr 2013
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    Might be worth your while having a chat with Lisa Cain at the mid Cornwall school of jewellery. apparently she is one of the foremost teachers of PMC. Here is a link to her: http://www.mcsj.co.uk/lisa-cain-tutor-profile.html
    She is also director of the PMC guild so may well have come across this problem before?

  8. #8
    Join Date
    Mar 2010
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    Braunton, North Devon
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    I have been using metal clay for about ten years. What you are seeing is actually quite normal for fired silver clay. You need to remember that when fired, it doesn't liquefy, so it's molecular structure is not the same as, say, a cast piece or a piece of rolled sheet. Yes, the molecules "sinter" at the required temperature, but the structure is in essence porous, like microscopic honeycomb, if you will. Because of this, it will never be as strong or tough as rolled or cast metal. I have no doubt that my kiln is firing correctly, but I bet if a tried hard enough with pliers I could break off a piece of fired metal clay and it would look the same inside as you describe - slightly chalky.
    It's one of the down sides to the medium, sadly.

    Sarah

  9. #9
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    Mar 2013
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    Thank-you for your reply Caroline. I haven't used a burnishing tool before and when I looked online there seemed to be different types. Is there any type in particular you'd recommend for burnishing the back of a cufflink before soldering? Many thanks

  10. #10
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    Mar 2013
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    Thank-you V, Steve and Sarah for your very helpful replies. I will contact Lisa Cain as suggested to see if she has any insights. I think I'm beginning to understand that fired silver is not the same as cast and that extra measures are needed.
    V, I've been firing at 750 degrees for 15 minutes although from what you said and the very helpful link you posted it seems I could go to a higher temperature for longer. I'm still mystified why it's been ok up until now though! I haven't used a hammer before although one did come with the package of equipment and materials that I originally bought when I started with silver clay, but there was no indication in the online course how to use it.

    Many thanks

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