Plastics options for molding

Question

I am creating a sword for cosplay, and I need the material used to be clear, rigid, and lightweight, and to cure properly in such a thin mould (and can be poured into the mould I have, as I'd prefer to not start an entirely new process, although I'm open to any suggestions).

I have a mould made from a platinum-cure silicone rubber. It's a pretty simple shape with a 3mm thickness.

^{To the left, the blade will be made by connecting multiple together. The center: I'm pointing at where I'll put the LED strip, facing outwards to light up the plastic. To the right: the mould used}

I have attempted to use a fast cast urethane resin, with a shore D hardness 72 that is clear.

The material I used is mass sensitive (cures better at a greater volume/thickness), and does not get very rigid since the mould is quite thin.

Are there any other types of plastics I could use that meet my needs?
I can include pictures of the shape I've tried to cast if that would help, or links to the products I've used so far.

Answer 1

The key issue here is probably that your trying to mold something so thin.

You can get round the curing issue with two part casting resin by using an external heat source. I regularly cast very thin pieces using generic two part clear casting resin by mixing the resin in a jug that's allowed to sit in a bowl of hot water for several minutes and then leaving the mold next to a heat source.

However, objects that are cast so thinly will either be brittle if mixed for hardness, or will bend\warp if mixed to avoid being brittle.

No resin on the market that I am aware of will be suitable for anything the size of a sword of that description. It's one of the reasons that cosplayers typically use other materials.

If you want to use resin, my suggestion would be to purchase a clear acrylic rod to run down the center of the mold to give it strength, and then to cast the individual pieces to fit around it, and to make the sword considerably thicker.

I would caution that even if you are successful you may have difficulty being allowed to carry a resin sword at a competition or a convention. Your sword would have a very thin, and could fall foul of rules prohibiting anything that can carry an edge. If the edge of your blade is less than about 5mm thick, it could be classed as a "real" weapon. A resin dagger with a 3mm edge absolutely can kill someone. It would also likely shatter if you knocked it against pretty much anything hard.

Your model is too thin to vacuum form, you could possibly pay to have it 3D printed using transparent PLA but it wouldn't be perfectly transparent, or you could cut it from single sheet of clear acrylic.

If I were you I would look at the reason why you wanted it to be clear. For example, if it's supposed to be made of ice you may be better off cutting it from acrylic and painting it to look like ice.

If you want the sword to be "invisible" such as Death's blade from the Discworld franchise, then consider using knit wire to represent the outline of a blade.

I don't believe that the material that you want, for the purpose that you want, exists.