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Author Topic: Brittle clay  (Read 11145 times)

MrsH

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Brittle clay
« on: April 11, 2014, 05:06:42 PM »
Hi,

I'm stuck!

I'm using Premo Sculpey and it's really brittle after baking. I've definitely conditioned it enough as all the clay goes through the pasta machine a ton of times and it's really soft.

I'm baking in a halogen oven at 130 for one hour, I know the temp is right as I have an oven thermometer and it reads 130.

So I'm stuck as I can't think of any reason that the clay is brittle. All the clay is new bought very recently so it can't be that. I've baked a lot of different things in different colours and they all seem to break after firing.   

Any advice would be welcome.

shelleym

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Re: Brittle clay
« Reply #1 on: April 11, 2014, 06:58:27 PM »
I often have the same problem. I've found fimo (classic and soft) and premo all just as bad as each other for brittleness recently. Definitely since the formular change a few years back. I have just ordered a new halogen oven and fimo thermometer in the hope that part of the problem might be the temperature and my oven. The one clay I've found much better than others is Cernit. I may have to switch! But I'm going to try the new halogen oven and thermometer first.

The only thing I can suggest is testing with a different thermometer and at different places in the oven to see how it goes. I hope someone else can come up with a suggestion.

Shelley



JennyM

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Re: Brittle clay
« Reply #2 on: April 14, 2014, 03:17:49 AM »
Can I just ask how thin are the clay pieces you are making? I use Premo and generally don't have any problems with it. Do you use an oven thermometer with your halogen oven? Modern appliances are notorious for being inaccurate. Just because the oven is set to a certain temperature doesn't mean it is heating to the temperature you want. Stores specialising in kitchen wares usually oven thermometers. I wouldn't be without mine.
Premo is generally flexible after its baked even if it is thin. I suspect its a temperature problem.

ickledookie

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Re: Brittle clay
« Reply #3 on: April 14, 2014, 01:34:30 PM »
Last summer I had a lot of connectors go brittle & snap! I don't think it's you at all as it happened to another friend who makes polymer clay beads. I reckon it's a bad batch of clay & not you as all my stuff is fine now.  ;)

ejralph

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Re: Brittle clay
« Reply #4 on: April 14, 2014, 06:04:14 PM »
I'm with Shelley on this one - I think that Premo just isn't as strong since the formulations changed some years back.

Now, I tend to equate Premo with Fimo Soft in terms of strength. Fimo Classic is much stronger than both, but not as strong as Cernit, which is tough as old boots.

So I think it really depends on what you are making. If you are going for flat-ish pendants and that type of thing, then Fimo Classic or preferably Cernit is probably a wise choice.

For solid shapes without protrusions, such as solid beads etc, then really any of the clays will be fine.

Emma
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Peter

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Re: Brittle clay
« Reply #5 on: April 14, 2014, 06:36:59 PM »
Have to agree with Emma. I use mostly Fimo Soft and that is OK because I mostly make solid beads (15mm +). However, even I have noticed that I have to be more careful drilling after the bead has cooked or the exit hole for the drill bit will "flake" and I won't get a clean hole.

shelleym

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Re: Brittle clay
« Reply #6 on: April 14, 2014, 06:50:30 PM »
Fimo classic though slightly stronger still isn't anywhere near as strong as it used to be IMO. Have you had any of the newer clay in yet of the fimo 'professional' or whatever they are calling it Emma? I am wondering what that will be like. I have a ton of fimo soft and premo which I will just have to use up. I have even had complete beads that got caught on something and they have smashed which they never used to do. I am going for thicker and thicker pieces and will just use up the clay I have and probably move to Cernit, or possibly the newer fimo if that's better. Would love to know when it's coming out and what it's like!!

Not long ago I did a drill test. Small bits of clay on thickest setting - small cut out round shapes. Drilled them straight  through to make a hole when baked. Very old fimo and cernit performed the best.  I have never tried Kato (not sure I could handle it from what I've heard it's quite firm to start with) and haven't tried Pardo. But certainly between fimo classic, soft, premo and cernit and various mixes of the clays  Cernit was without doubt the strongest and had the cleanest hole.

Shelley

MrsH

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Re: Brittle clay
« Reply #7 on: April 17, 2014, 05:20:54 PM »
Thanks for all the replies! It's good to hear I'm not the only one suffering.

The frustrating thing is I have invested in a lot of Premo as I knew I would be making a lot as I learnt to use polymer. So I've a ton of Premo to use up, but after it's gone I'm going to try Cernit as that seems to be coming out on top from what I'm reading on the forum. The thing that Premo have though is such a good range of colours too!

Anyway, back to brittle clay. I'm making buttons for a project so they are round and about 3mm thick and 20mm across. I'm making two holes in them for the thread with a small straw before I bake . The design has an extruded front and then backed with a solid sheet of clay, so I thought it would be strong enough. I don't want to make the buttons thicker as that makes them look and feel clumsy and amateur!

The temp is definitely right as I'm using an oven thermometer which I've had for a while and it's always worked well. I'm loving the halogen oven too, though being very careful with the heat!


ejralph

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Re: Brittle clay
« Reply #8 on: April 19, 2014, 11:55:36 AM »
It is frustrating how the clays are generally a little weaker these days.

You can try some experiments though with your Premo.

1. Try eeking up the heat a little. Do tests maybe rather than risk finished makes. But even 5 degrees hotter might be something the clay will let you get away with and be somewhat stronger for it. I find with flat items, I can get away with going a little hotter often. You might want to tent the clay though to protect the surface from the heat.

Be sure to check the increased heat doesnt adversely affect the colours.

2. Try mixing in a solid clay softener.
Fimo Mixquick or Cernit Softmix (I'm out of stock on both right now, but we do usually carry them at EJR Beads)

These solid softeners actually can add increased flexibility and therefore strength, to the baked clay. You mix about 1/3 softener to 2/3s clay. Maybe adding some of the Cernit softener to the Premo will give you a better strength overall? Again, do some text tiles to check.

Either way, I think 3 mm thick for a Premo button is pushing the envelope slightly in terms of expectations if you're looking for full functionality. If you could consider 1 or 2 mm thicker than that and find a way to embrace the chunkyness somehow, you might end up with a stronger product overall.

That isn't to say that 3 mm buttons can't be done - but I'd definitely try Cernit for that.

Emma
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Karolina.S

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Re: Brittle clay
« Reply #9 on: April 19, 2014, 06:56:59 PM »
I noticed by accident that i f you coat the item with an layer of TLS it will be really strong and flexibel.

I tried this with a 1 mm piece one day and i had a hard time breaking it. I spread the TLS so thin that it was not visable at all.
Timrċ in the north of Sweden. Always with my polymer clay eyes open.
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Carrie

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Re: Brittle clay
« Reply #10 on: April 19, 2014, 08:00:23 PM »
That's useful to know, Karolina!

ejralph

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Re: Brittle clay
« Reply #11 on: April 20, 2014, 05:25:35 PM »
What a great tip Karolina, thanks for sharing!

Emma
Emma from Sunny Sussex, UK
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jewelray

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Re: Brittle clay
« Reply #12 on: June 07, 2014, 04:27:30 PM »
Hi.  Can you tell me what TLS is please as I have had the same problem with Fimo Classic for really thin beads.  I have already strung them but only have touch them and they break.  Thanks.  RayM

Carrie

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Re: Brittle clay
« Reply #13 on: June 07, 2014, 04:48:30 PM »
It is Translucent Liquid Sculpey - liquid clay  :) 

lt's useful to have liquid clay on hand - Liquid Fimo or TLS - as they will make a good bond between raw and baked clay.  Karolina's discovery sounds good too....it would probably work with any liquid clay.

Going back to buttons, if they were made thicker and looked a bit chunky then rounding the edges would disguise that very well.

Karolina.S

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Re: Brittle clay
« Reply #14 on: June 07, 2014, 07:47:40 PM »
:)
Timrċ in the north of Sweden. Always with my polymer clay eyes open.
http://www.flickr.com/photos/77424684@N04/ http://www.facebook.com/Hobbyrian