Fake cum - what is it?

[joelucas]

In a lot of cum shot pictures (not videos), the cum shots on a girls face, boobs or stomach really doesn't look like cum. A lot of them do show real cum, and obviously those shots that show the stream being ejaculated are real, and most of the vids are real. With the exception of those "monster" cum shots where it looks like a fire hose - those are fake.

What I'm wondering is what do they use for the "fake" cum in the still photos? Anyone here in the porn business that can enlighten us?