I do a fair amount of casting in both hard plasters like Ultracal 30 and various urethane resins. I always cast with a ‘no scrape’ method, where instead of laboriously dragging a smoothing tool across the open face of a partially set mold, I simply smooth a cover down over the poured mold and leave it to set.
This method relies on the casting material forming a hydraulic seal between the mold and the cover. It’s quick and easy and usually provides casts with nice smooth bases, however it does have some disadvantages:
- To get a good seal, you need to over fill the mold slightly, resulting in wastage of the casting material.
- You need to clean the cover afterwards. In the past I’ve always used the front of cheap CD jewel cases which plaster and resin adhere to quite well. Meaning cleaning can be tedious and will scratch the cover, resulting in more casting material sticking on the next cast!
- Both your mold and cover must be quite flat and preferably level for a good seal. Again cheap CD jewel cases are less than ideal because many of them are subtley warped which mean air can sneak in under the edges.
- You’re limited to molds roughly the same size as your cover.
Recently I’ve started molding my 1930’s building facade in plaster, and it’s considerably larger than a CD jewel cover which means I’ve had to find an alternate source of cheap, flat, transparent casting covers.
Here in New Zealand, $5nz will get you a couple of cheap photo frames from the Warehouse. The glass simply falls out of these and you’ll also be left with a nice wooden frame you can use to build display bases for your Bloodbowl teams or Mordheim warbands.
After doing several casts with these glass sheets I’m regretting I didn’t try using glass years ago. Mainly because with a window scraping razor (for house painting) they’re very easy to clean and don’t get damaged at all. Once my current stash of CD jewel cases has been consumed I suspect I’ll change over to using glass covers for all my casting.