Welcome to the community aitek. Hope you enjoy your stay. [excited]
That's excellent artwork, i love the ombience produced by the lighting.
You can try Multiply, but
IMO i think you simply have to make the cracks black. Unless you intend on creating a thickness effect for the porcelin.
I'm not sure if you're familiar with the Dsiplace filter or not but...
One thing i might also do is apply the Displace filter to the cracks layer. If they're not all on one layer, you'd have to create a merged copy of them to apply the Displace filter to. Simply save a duplicate of the image with the woman by herself, with no cracks, and as a flattened PSD file. Then open the displace filter and apply that file to the cracks layer.
What this will do is make the cracks mold to match the curves of her face and body.
PS: "AutoFX" has a plugin that creates that exact effect. Can't tell if that was used to make this image or not, but it doesn't matter really. It's a great looking image/effect anyway.