I need an epoxy that won't yellow when heated (to 230 F) - please help.


I'm doing some craft projects where I'm attaching small LED lights behind pieces of glass and crystal-type stones.  Then I'm adding some decorative elements using Fimo clay.  The problem is, due to certain LED and clay placement, I need to bake the clay *after* connecting it to the glass/stones.  So the entire piece goes in the oven.  The lights and solder hold up just fine to the 230 degrees Fahrenheit for 30 minutes.  My epoxy, however, turns very yellow.  If I have a blue piece of glass with a white LED epoxied to it, it shines very much green. 

So basically, does anybody know of an epoxy that won't go yellow when exposed to heat?

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Conventional epoxies won't like temperatures over 100 C, and will colour. High temp. epoxies exist, from folks like Permabond - maybe West System 'poxies will work.
Kiteman6 years ago
Are you sure it's the epoxy turning yellow, and not the plastic of the LEDs?

Try baking a single LED and a separate blob of the epoxy stuck to a shard of glass and see which changes.
also, it might just be the blue glass has properties of filtering out the light in a way that it just appears yellow. Red glass may look orange, as LEDs are not a full spectrum white light.
aliasjanedoe (author)  caitlinsdad6 years ago
I can see the yellow of the epoxy through the glass when the light is not even turned on. My problem is 100% due to the epoxy yellowing when heated. If you have some epoxy on hand, go stick a dried blop of it in your oven for half an hour at 230F. You'll see what I'm talking about. It turns a rather bold yellow. If you try this and it doesn't yellow, please let us all know what brand you tested.
aliasjanedoe (author)  Kiteman6 years ago
Oh, forgot to mention, I also baked a plain piece of glass and one with epoxy to make sure it wasn't something about the fogginess of the glass that was reacting. The glass alone was just fine. The blop of epoxy on the other piece was a bold yellow spot when it came out of the oven. I also tested epoxies on other things. It's always the epoxy that goes yellow, but I've only tried off-the-shelf hardware store 2-part epoxies so far. The little ones, not the more expensive resins that come in the cans.
aliasjanedoe (author)  Kiteman6 years ago
I've already done control tests. I'm 100% sure that it's the epoxy turning yellow. The LEDs handle the heat just fine as far as I can tell; no noticeable change to them.
caitlinsdad6 years ago
Maybe you could experiment with some superglues to see if that works, at least it will leave a thinner coating or smaller attachment points. Ring or spot the epoxy away from the lens/focal point of the LED. Create a mount to hold the LED or leads in place. Use air-drying clay instead. Good luck.
aliasjanedoe (author)  caitlinsdad6 years ago
Thanks for the tips, but that won't solve my problem. I really do need an epoxy or resin of some kind for my purposes. There's got to be one out there that can take a bit of heat.
A little googling reveals that the yellowing may be caused by exposure to UV light. Most consumer or less expensive epoxies will not contain the UV protected formulation. The are custom made industrial epoxies that don't yellow and do hold up to 250 F heat. I don't know if you need to order a 55 gal drum of that stuff. You might have to experiment.
aliasjanedoe (author)  caitlinsdad6 years ago
I've no problem with the hint of yellow that just happens over time to epoxies that claim to be "water clear". It's subtle and not an issue. It's the heat of the oven that's causing the drastic and sudden yellowing.

I've googled a bit also, and I just don't know what to take the risk on if I experiment. The amounts are way more than I need of the ones that seem likely to work best (not 55 gallons, but still about $60 worth of product). And the fine print for pretty much everything says it's "light amber" in color or some such, and it's hard to find anything that talks about temperatures and further yellowing. I simply don't have the money to try them out.

No chance anybody here has some the large containers of resins for other projects and would be willing to smear a tiny bit on something and stick it in the oven?
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