Clear Casting Question

peteskywalker

New Member
Hi Guys

Had my first try at clear casting and it didn't go to well and wanted to see if you guys could help.

I intend to fill a perspex tube with clear resin to make a Darth Vader in Bacta Tank. I used hot glue to set another flat part of perspex to be removed after the first layer of resin.

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I loosely wrapped the clingfilm around the tube to stop any resin from getting on the side and also placed it on the top to stop any debris getting in.

I used Clear Casting Polyester Resin that was advertised as low shrinkage but as you can see thats not the case. I can deal with the shrinkage but sadly the casting cracked the perspex.

Anyone have any tips on how to prevent this or any recommendations of resin to use?


oNjN7R.jpg


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Hi
Not sure if I understood correctly. The plastic wrap wrinkles in the pic might be confusing me a little.
Never used a clear polyester resin that said "low shrinkage" but I guess it will be similar to what we use here.
First of all, as you might know, polyester resin (clear or normal) shrinks as it hardens with a strong exothermal reaction (liberates heat).
And this can cause cracking if the reaction heats up too much. With normal polyester one would try to solve this by adding a filler in first instance, but that wont work for the clear resin, you would loose the clearness.
All this asuming you are working with the correct ratios
I´m not sure if your "first layer" means filling it up to the top, or that you are filling the tube by parts (smaller batches).

Clear polyester resin (at least the two or three brands I use) has a limit to the quantity you can cathalize at one time without experimenting cracking or yellowing issues.
This quantity can variate depending on room temp. The higher it is, more chances it cracks.

So, all you can do is play with the following parameters: as I see it:

The quantity of resin you cathalize at one time. If its cracking try with smaller batches. The downside can be that "pour lines" apear in the final piece. Try to pour again when the resin is still tacky. Too soon migh cause that the exother. reaction adds up, and too late can give other issues.
Try to cover the tube between pours to avoid dust, microdust will allways be there.

Variate the cathalyst ratio. For example, the clear pol. resins I use go with 1.5% when you are mixing batches smaller than 200 gr. And if you go for bigger batches you can lower the ratio down to 1 or 0.5% (the limit on the low side) to try to avoid cracking etc...

Try to cool down the resin before mixing and pourig, the room and the mold.

Some years ago I casted several clear feet (and part of leg). It was a 2,5kg pour each. In cold winter, with the cathalyst at 0.5% I got good castings.
The castings where exposed permanently in a public place, and some where stolen/broken,, so I was asked to cast new pieces...in hot summer.
No way, couldn´t get a perfect one. I cooled down the resin, poured in the molds placed in buckets full of ice. Always a crack somewhere that had to be fixed as we could.

Polyester resin can be very tricky for bigger castings.

You could try with other materials: PU clear resin, or Epoxy but I´d say most of them have the same problem: Exotherm reaction, cracks, yellowing...
And shrinkage is partt of clear polyester´s process.

Good luck
 
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Does it have to be resin? How about filling with a clear gel, like a body wash gel. It is shelf stable if sealed (to prevent drying out) and non-permanent if you change your mind on the figure's position, paint job or type.
 
Polyester resin is generally kept liquidy with incredibly harsh solvents that will destroy most plastics. You're probably going to want a platinum silicone mold to withstand the chemistry and the heat it gives off as it kicks.

An epoxy may be friendlier, but it'll also yellow eventually no matter how many UV stabilizers they put in it and unless you can pressure cast something that size, you'll never get all the bubbles out.
 
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