[Paul Reid]

Hello – I hope someone can help me!

I have recently bought so sphere silicone molds; they are good quality silicone, quite thick and stable so hold their shape.

To see what they cast like I used the bottom half of a dome and used alcohol inks as usual. When I checked that the resin had cured there was ink on the outside of the dome that was laying on top of the resin as if it had been added afterward, lots of patches and the texture is terrible. The mould has a clear shiny surface inside so I was expecting a nice clear casting. These moulds are quite big so even a dome is quite a lots of resin to waste.

I don’t want to try another dome or the sphere until I can check that I am not doing something wrong.

I am using clear-casting polyester resin and have created some lovely pieces using different moulds so I know the resin is good. If anyone has any hints of tricks for casting domes/spheres with alcohol inks I would be really grateful!

Thank you in advance.

Paul

[Katherine Swift]

Hi Paul,

Can you link to a picture of the problem?

[Paul Reid]

Hi Katherine

I have sent through the picture.

Thanks for your time.

Paul

[Katherine Swift]

Picture of casting:

[Katherine Swift]

Thanks Paul, this helps!

Your polyester casting resin is getting too hot and shrinking away from the mold. Polyester resin is weird in that the amount of catalyst you use not only depends on the amount of resin, but also the depth of the pour. I don’t know how you are gauging the amount of catalyst to use, but I would start with going to the manufacturer. If you are already using their recommendations, back the amount of catalyst off by 20 to 25 percent, then try again.

[Paul Reid]

Hi Katherine

Thanks very much for your advice. I am using the recommended 2% so I will reduce this slightly and see how it goes.

Thanks again!

Paul

[Paul Reid]

Hi Katherine

Sorry to bother you again. I am still having issues I am afraid.

I have reduced the hardener by approximately half and I am still getting wrinkles around the sides. They feel thinner but there are more and they feel spread out.

I tried using 3 different moulds (silicone catering mold/silicone arts sphere mold/plastic bowl with domed shape) they all had this issue.

I had a one-off a while ago where the resin was just starting to go off so I poured it into the plastic bowl mentioned above and it came out smooth! That was with the recommended hardener proportions.

Any ideas would be gratefully received.

Regards

Paul

[Katherine Swift]

Hi Paul,

It still sounds like your resin is getting too hot. Are you pouring this in layers? The heat is additive. You should add less hardener per layer.

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