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13 Apr 2013 - 21:18100912
Resin casting failure
Hi CI folks,

I spent £16 on Gedeo clear resin, as shown here:

I'm trying to cast a round dome with a flat back - it's 7.5cm in diameter and 2cm thick at the highest point. My first attempt I used 40mL resin and 20mL hardener, having found out the capacity of the alginate mould using water. I mixed the resin and hardener together until they were clear, as the instructions stated. The mould I had cast 2 days previously.

I cleaned the mould using kitchen towel prior to adding the resin. I left it to harden for 24 hours, and popped it out only to find that there were white milky streaks throughout the upper surface and several little crevices running along surface. I did the original alginate mould using a plastic craft bauble pressed into the container - I was expecting air bubbles but not crevices. I tried sanding it but it went about 0.5cm deep. The back surface was clear, it was only the dome bit that had this.

I had another go, thinking perhaps it was because I'd left the mould for a day or two. But it happened again on the second attempt using a fresh mould. I've now run out hardener because they only give you 50mL in the bottle.

My internet searching on this has been a bit fruitless, so if anyone can give me an idea as to what I've done wrong so I can avoid further expenditure/wasted time, that would be great!

Thanks guys

Last edited by madmazda86 (13 Apr 2013 - 21:28)
13 Apr 2013 - 21:30100914
My recent experiments with custom moulds have so far been also been failures, but in different ways - cloudyness and rough surface where it met the mould, and thats using food grade 2 part silicone putty. I did have one that went really odd in my pre-made gem moulds, but I never did work out why.

If you're going to be using a lot of that resin http://www.metalclay.co.uk/products/Crystal-Resin-750ml-%2826oz%29.html were by far the cheapest I'd found for the Gedeo - about £25 for 750ml, or £14.75 for a 300ml one. Shippings £2 for orders under £30.

Not so useful for solving the problem, but cheaper if you need to restock

Edit: http://www.network54.com/Forum/42978/thread/1127634429/last-1130334231/Resin+and+Alginate+casting and http://www.therpf.com/f9/casting-alginate-resin-76019/ suggests its a common issue to do with the moisture in the alginate.

Last edited by Junta (13 Apr 2013 - 21:36)
13 Apr 2013 - 21:32100915
I have no experience with this myself, but did a quick google and it suggests it might be that the room it's curing in is too cold?


14 Apr 2013 - 18:52100954
I've cast resin outside in the garage while it was snowing before, but that was with the hardcore type, in other words the sort of resin you would use for fibreglassing garage roofs. My dad usually advises letting it go off in a warm environment mainly because it will set faster.

It depends on the kind of mould too, some resins will actually cloud over depending on what sort of mould it's placed inside but this doesnt look like your typical clouding since its affected the surface.

Maybe you could try a 50/50 mix of resin and hardener and see if that makes any difference as that's what I've seen most, if not all resin users on youtube do including myself. But I assume that you've been going from the instructions on the pack of resin.

There's my thoughts, they're not exactly helpful but it might help you out if you decide to try again with different methods. I really hope it works out for you though - resin can be a pain!


Easy Cast is a popular brand amongst resin users, usually those who make jewellery and charms because they want a nice clear finish. Just remember to let the resin sit and de-gas for a few minutes if you don't already

Last edited by Angel Tear (14 Apr 2013 - 18:55)
14 Apr 2013 - 22:53100973
Thanks for the advice, guys. In the end, some further Google-fu found these:

Orthodontics textbook

Turns out epoxy resin is just plain NOT suitable for alginate moulds, as Junta suggested. Further supported by the fact that the dregs of resin that I had left in the plastic cup I used for mixing have dried clear with none of this clouding. I should've watched some Youtube videos! In no place in the provided instructions does it tell you this. Oh well!

Last edited by madmazda86 (14 Apr 2013 - 22:54)
15 Apr 2013 - 09:53100983
Sorry to hear about your moulds not being suitable for the resin! At least you managed to find a reason for it. ;;

I don't know if you've had a look already, but maybe you'll be able to use one of these moulds to save casting your own? (Might be a bit thick but the diameter is about right.) I've used them multiple times with EasyCast epoxy resin and had no problems.

16 Apr 2013 - 20:39101108
Thanks for the suggestions! I've ordered one of those dome moulds and some more casting resin from MetalClays.co.uk that Junta linked. I looked at using my Dremel to cut up the plastic sphere I used for the moulds but it looks like the plastic will probably melt from the heat (I'll probably try it anyway after I've done this third round of casting just to see if it works XD)

So in total I've spent an entire month of my cosplay budget (£40) just on casting stuff. Le sigh. But it'll hopefully work this time!!

17 Apr 2013 - 23:41101173
I know this is late but silicon moulds work a treat with epoxy resin.

I've found food grade moulds for cakes excellent - you can get them quite cheap and because they are so flexible the resin just pops out when cured.

19 Apr 2013 - 07:15101248
Alginate is for plaster only, and only for straight after you've already taken the mould, it starts to shrink very quickly.

All your resin moulds should be done in silicone, you can read my journal entry on resin casts here, and how to get shiny vs. cloudy textures


My God. Its full of stars
19 Apr 2013 - 07:17101249
You should also heat your mould up before casting into it. Put it in your oven at a very low temperature to warm it up for 30minutes prior, then pour in your resin.

Unfortunately you probably shouldn't leave it in the oven once you've poured resin in it unless you have access to an oven not used for cooking! But the silicone mould in there should be fine, especially if you use a platinum silicone

My God. Its full of stars
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