I needed to make copies of a small item I had printed out, so I had to have a casting vessel = something to place the item in and to pour silicone over it to make a cast. I used cassete tape cases - they are straight and smooth and will leave no gaps - or so I thought. I stuck them together with sticky tape. The bonus is that you can fit more cassete tape cases into the vessel if you need to adjust the width or breadth for economy.
Materials / tools used:
6 cassete tape cases