Thought I would test my theory on the bumper caps as well.
For some reason ( that someone here may be aware of ) - every Stern cap appears to be available as a repro except these
I also wanted to try a material 'better' to work with than cellophane - so I bought some sheets of RED polycarbonate sheets from my local art supplier , it is like the covers on common office document folders BUT is smooth faced as opposed to a rough feel. You can see in this image it is still see-through but.
It is slightly easier to cut as it is thick and holds some shape while cutting.
In the end I cut the heart shape out of it, then stuck 2 layers of red cellophane to the side that would be facing up against the bumper plastic - I could stick any old shape of cellophane to it as it was simple to cut around the edge of this polycarbonate to trim the cellophane to shape.
Below LEFT is the initial result....right is one of my 'un-touched' caps.
Here is a look at the cap image from IPDB.
So I guess mine is now a little closer to this
I would like to try a couple of light but solid coats of red with the airbrush on TOP of the cap as well but unsure how this would look?
Gav ?
