The romans mad portrait paintings from a durable mixture of pigment and hot wax. what was this mixture called?

The mixture is called ENCAUSTIC.
Encaustic painting involves using heated bees wax to which coloured pigments have been added. The liquid paste is usually applied to the surface of  prepared wood such as canvas. The method is also called hot wax painting. 

Photography has changed its subject matter quite a lot over the past few years. in the 1800's, it was considered normal for families to have  post mortem photos of their loved ones, and now that would be completely unacceptable. i think that photographers have always pushed boundaries and have been eager to capture everything, it is just society that changes their boundaries.