casting help

[triw51]

I tried to cast some wood pieces for a bowl using similar 41. I mixed the resin according to directions and added some brass powder (approx. 1 1/2 teaspoons to 2 cups of resin). The resin turned emerald green and had cracks in between the wood.
Could this be a chemical reaction between the brass and the resin? I cast some colored pencils in that resin last week and no problem so I don't think it is the resin. Any ideas what caused the color change and cracks?
I tried to up load pictures but can not get it to work.

Thank you for any help. William

 

[Curly]

William I have no idea about the green but PR shrinks a little as it cures so isn't usually a good choice for resin/wood casting especially in larger sizes. That's why Alumilite and epoxy get used for them. Negligible shrinkage.

 

[robutacion]

Have you ever used that brass powder with that resin before...?

From what you've said, the resin seemed to have worked OK just before so I would suspect that that particular brass powder did react and oxidise with the heat of the resin curing. The green colours are the oxidised brass.

I would suggest you try a tiny small amount of that resin with some of that same brass powder, stir well and fast and let is set, a little waste but that will give you and answer the one way or the other...!

Good luck.

Cheers
George

 

[triw51]

I got the pictures to load. You can see the cracks and that it broke while I turned it.

 

[robutacion]

Wrong resin for that type of work, or you have to reduce the hardener to 1/4 of the recommended amount and be willing to wait a few days for it to set.

Any of the based Polyester type resins that cure at extremely hot temperatures is not a good choice for blanks that require a fair amount of resin, it will crack every time, even if the wood or whatever you embedded in that resin is humidity free, therefore properly dry or even stabilised.

You have at least, 2 issues with that blank, the wrong type of resin and a reaction to the brass powder you used.

Have you tried to do the test I mention previously...?

Cheers
George

 

[Bob Wemm]

Hi Mate, not really sure about this but I have trouble with cracking if I pour a large amount of resin.
If I need a big lot then I do several pours, allowing it to cool down before the next pour.
Probably talking out of the top of my head, but just my 2 bob's worth.

Bob

 

[triw51]

George due to the rain the last few days I have not tried the test. Waiting for it to dry out a bit first. Thank you for the information.

Bob thank you I was thinking of doing several pours instead of one. One reason being I had trouble with the wood floating. When I did a colored pencil poured with resin the weed did not float so am learning as I go

 

[Skie_M]

Pour the mold partially full and let it set till it cools a bit ... then add your wood and pour till the wood barely starts to float (add your internal mold to hold wood in place and weight it down), and let it set some more till it cools again ... continue pouring in stages till your mold is full or as full as it needs to be.

Once the final pour is made, you may want to keep your casting in a hotbox to allow the entire molding to cool off slowly and gradually... this need will vary from one resin to another.


Using a resin or epoxy that has very little shrinkage will be an essential item for large pours that contain things that will have little to no expansion/contraction from the heat.

If your wood had water content in it, that may be the source of your adverse reaction with the brass powder creating the green color.

Am thinking of using some copper pentahyrate in alumilite, just to see what may happen ... should be very interesting. (don't try this, this stuff is DEFINITELY poisonous...)

 

[Skie_M]

OK ... no steaming, thousands of tiny bubbles, no color bleeding, and the crystals aren't melting ... (The bubbles are from the mixing, I just recently poured it, they will rise up out of the molding over the next hour or so as it sets.)


I know brass shavings didn't react with my alumilite either ...