Hi Roger
Perspex is a trade name owned by ICI but is commonly used instead of acrylic which is chemically called Poly(methyl methacrylate).
Other comon names (mostly trade names) for acryilic are Policril, Plexiglas, Gavrieli, Vitroflex, Limacryl, R-Cast, Per-Clax, Perspex, Plazcryl, Acrylex, Acrylite, Acrylplast, Altuglas, Polycast, Oroglass, Optix and Lucite.
Acrylic is ideal for the sacrificial covering you describe and very cost effective in small amounts. It can be easily bonded with clear silicon.