Jeremy Randall gives a very detailed description on measuring the specific gravity of Terra Sigillata in this video on the Ceramic Arts Daily site.  He makes it seem almost possible...

Karen says there is a graduated cylinder in Hodson which I will retrieve for our use as she says it has been languishing on a shelf over there for a long time.

http://ceramicartsdaily.org/pottery-making-techniques/ceramic-decorating-techniques/pottery-video-of-the-week-how-to-mix-decant-and-troubleshoot-terra-sigillata/

Ann