old photo origins


This is a photo of mum (aged 18 months) with her brother, Robert and big sister, Joan. I've always loved its vintage 'cute kids' appeal, but recently took an interest in its origins. It was taken in 1936 towards the end of the Great Depression. Even though there were seven more siblings to follow, this is one of the few portraits the family could afford. It was taken by (local photographer) Francis Whitehead - his studio in Ipswich was the longest continuously family owned studio in Australia (before it sold in 2001). From what I can tell, it's a paper print encased in some sort of clear resin, with a metal back and stand. It's also possible that it's been printed straight onto metal with a resin overlay. The surface is glossy and easily scratched. I thought I'd find lots of online info, or some similar photos but...I'm stuck. Seems like there were numerous photographic processing techniques in the mid-1930's and it's hard to pinpoint exactly where this picture fits in. One thing's for sure, given the long exposure time (anywhere from 15 to 30 seconds), the children were either very well-behaved, or simply in awe of the "technology" of the time. 

Perhaps you've got a similar photo in your family, or you can point me in the direction of some antique photo expertise? All assistance greatly appreciated...and any stories about old photos are very welcomed!