Cleaning the flash from the new Super Barn castings wasn't as tiresome as I had feared - those big windows make a huge difference to how long it takes.
It also helped that they had been cast with very little excess resin so the flash was extremely thin and easily removed with the tip of a blade.
With the open back mould there will always be a film of resin trapped between the mould and the perspex sheet but there can be quite a variation in the thickness.
With a poor cast it can be up to 0.10" thick sometimes but with a good one, as these were, it's so gossamer thin it can be virtually transparent.
I'm looking forward to gluing the bits together later this week if I get a chance.