The Mask (Punch)

So for my mask I have made my design of my intake of Punch from Punch and Judie. So far I have put about 7-8 layers of non-thickened Latex on my mask and 6-7 layers with thickener. Next I need to add colour so now I am. I am now doing a layer of white Acrylic thickened Latex mix. This will make the colours look brighter. For the colours I will make a yellow Acrylic Latex mix for the first layer of colour and will cover the mask with 3 layers when its dry.
These are the colours I have used on the Punch mask. When doing the pattern i just made it up on the mask.
I am happy with my pattern on this mask. I now think I'm going to make a black line around the edge of the pattern, but I don't know what to do it with out of paint it or draw it with a black sharpie.