Hi Ellen. I generally like to use leather dyes for my masks as it is alcohol based and will penetrate the leather easily. This is safe for skin contact, however if the mask gets wet after the first few days it may seep out, which can cause quite a problem if the dampness is caused by someones face sweating! Aside from that, for more delecate designs I will use acrylic paint, usually overtop of the dyes, as this helps the paint show up with fewer layers as it seals some of the pores on the leather. To prevent the dyes from seeping, and to protect the paint, I will then seal the mask in an acrylic sealer of the spray on variety. This also gives the masks a nice sheen and can be polished in the future, keeping it looking like new. Also to answer another question of yours, it is usually a good idea to also color the inside of the mask, that way even when it is not on the person's face, it can still be viewed like a work of art. If you did not color the back side of the mask, then the raw leather color could be seen through the eye holes and at different angles, which would look bad. Hope this helps!