Levin Auctioneering Co. Ltd Cinema Advertising Slide
From antiques to furniture a trip to the auctioneers was the offline version of popular internet auction sites. This company also took out paper advertising which can be seen on Kete Horowhenua (https://horowhenua.kete.net.nz/item/9d7d6049-c491-45ac-8c35-3a2b02e6c830) but they were then in a different location and under a different auctioneer. The printed advert was from the 1950s- it is believed that this slide was made later.
Unlike a newspaper which was read by one person at a time, a cinema slide was projected at the end of a film's intermission (later, when intermissions fell out of favour, they were often screened before the film began). The projectionist had to display and remove the slide in a few seconds- otherwise the heat from the projector's lamp would crack the glass!
Becoming a projectionist took around five years of on the job training- and preparing the advertising slides was one of the first jobs a trainee was entrusted with. Just don't crack the slides.....