bw1's comment is excellent...you can even do the effect with just latex, can stipple it on the skin in sections and then stretch the skin while applying heat with a hair drier...powder the latex after it's dry so it won't stick to itself, then relax the skin a voila! Instant wrinkles.

The spirit gum and cotton provide a stronger and more durable effect. You can strengthen the wrinkle effect with painted shadows and highlights.

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