I think I just need more practise to work out the 'tricks' to doing this, but I think I am probably stretching the practical uses of Instant Mold by attempting two-part casting. Don't get me wrong, it is possible - with care - but I think the whole idea of Instant Mold is quick and easy press moulding really.
Two-part moulding is a slightly more complicated and precise type of moulding and - to be honest - if you are going as far as taking the time to make a properly aligned two-piece mould you will probably want to make something you can keep and use a lot of times.
So, what went right?
Well the quality of the cast was good it captured the general shape of my original object very nicely. And using Milliput mean I had a really hard duplicate that I can sand or otherwise modify further.
So, what didn't go right?
Registration. I did try to make registration dimples in the Instant Mould so the two halves of the mould would come together precisely, but I just didn't do a good enough job. The two halves slipped when I tried to put them back together again with the Milliput inside and so the cast was mis-aligned...
Now, I could rescue this casting by cutting it down the middle and realigning the two pieces again. But that kinds makes the whole process of trying a two-part mould a but of a waste of time. I might as well have just moulded the two pieces separately and then stuck them together at the end...
|Alternative way of doing this (or how to rescue a failed two-part mould) is|
to simply revert to doing the casting as two single part moulds and then to
glue the resultant pieces together. Perhaps? :(
|The result of 'one piece' moulding the helmet parts. Now I don't have the|
alignment problem BUT I now have to clean up and glue the two halves
together. Not so cool!
But the good thing about Instant Mold is you can just melt it down again in boiling water and start again. And this time I would make better registration marks (dimples) in the mould so that the whole thing aligns better (hopefully).
...And then again, I'm starting to think that I might as well invest in a proper resin casting set if I am going to start to do more complex casting from a much more detailed original. The resin mould would also have a longer life and allow me to use cheaper resin as a casting medium rather than expensive Milliput...
|The Sylmasta Resin Casting Kit (£38). Perhaps the next|
step in my casting experimentation?
Well, I feel I learned a lot about what Instant Mold is good and not so good for. It's ideal for one-piece press moulding but not so ideal for larger more detailed 3D two-piece casting. You can do it at a pinch, but the whole idea of Instant Mold is that it's 'instant' and you use it to copy something quickly and then re-melt it to use it again for something else.
|My failed two-piece mould, melted back down to use again|
for another mould. Best attribute about Instant Mold.
It's definitely a great tool to have on your workbench and I will be experimenting with it again to see what else I can copy (and I will be trying out different casting mediums, like Green Stuff and even PollyFilla plaster). But I think I will invest in a resin casting kit as well.
Anyway, to end off this post, here's my fudged two-piece (two separate single castings) pith helmet. I glued the two pieces together to make the complete helmet with super glue. It's a passable rescue of my failed (proper) two-piece mould attempt, but it will do for my prototype figure I'm making!