Have you thought about aluminium?

I can see not getting to fancy with your experiment but without some sort of artwork I think that it is making it harder than it has to be to cast plain scales. With the amount of work to shape the wax you could already have a set from a sheet of metal.

I would shy away from the single piece idea. How are you going to run the sprues and vents from the mold? With two pieces you can put everything in the relatively hidden inside for less clean up. Soldering the halves together would be easy and unnoticeable.

Make your wax as smooth as you can because one of the neat things with investment casting is you get out what you put in. If you do it right every scratch will be reproduced perfectly.

I look forward to your results.

Tim