King George VI Period - Robes 10/- dull purple on chalk-surfaced paper 'By Authority' imprint block of 4 with lower two stamps never hinged & top two lightly hinged. Cat $175 for hinged.
Stamp Tricks and Tips: Chalk-Surfaced Papers | Sandafayre
Chalk-Surfaced Paper: Examples & Tips on Identification | The Stamp Forum (TSF)
SG233 3d Dull Reddish Purple/ Yellow DLR Chalk Surface Paper Unmounted Mint Edward VII Stamps
c.1879/ 85 De La Rue Dummy stamp in purple, corner pair. Unmounted on unwatermarked, chalk surfaced paper?
Kenya 1966-1971 SG#30, 1s30 Elephant Chalk-Surfaced Paper Used #F4416 | eBay