The images in this gallery were taken by my great-great uncle, Heinrich Schildknecht, an Austrian “alpine” photographer.
The 4″x5.75″ negatives were given to me by his grandson when I met him in Europe several years ago. It’s difficult to date them because the date that the photographer wrote on the envelope looks like it could either be 1919 or 1929. Now that I have a flatbed scanner with a transparency unit, I thought it was time to preserve them.
I remember asking his grandson whether or not he had his grandfather’s complete collection of negatives. He replied “No, my grandfather’s studio burned down”. I’m not surprised.
To the best of my knowledge, the items he gave me are made with a cellulose nitrate base. Most articles you read about this type of film give dire warnings that they are extremely flammable. The typical advice is to copy them, then dispose of them properly.
Two of the many signs that films are made of cellulose nitrate are the tendency to curl and turn amber as they age. Have a look at the picture of my negs. They definitely exhibit these characteristics. 
The ones that curl the most seem to have a thicker base, while the flat ones are almost as thin as paper.
In some cases, the experts warn, the emulsion becomes sticky and gives off a toxic gas. Luckily, mine do not have this problem, although the emulsion is flaking in places.
There are several ways to test these films to determine whether or not they are cellulose nitrate, as outlined in this excellent article: http://bit.ly/aAKaQi. I decided to try the burn test with a strip of each of the thin and thick bases.
With the fire department on speed dial, I headed outside in the snow, far from the house and lit ’em up. Yup -the thick base burned very quickly and crackled a bit like a sparkler. The thin base was a bit more sluggish, but also burned fairly quickly.
The safe assumption is that these are cellulose nitrate bases, so I’ll be doing the right thing and disposing after copying. I may even wait for a fireworks celebration and have my own backyard spectacle. If a reader more knowledgeable than I has more insight into these negs, I would appreciate a comment.
Amazingly, from the timeline in this document (http://bit.ly/d4ysrt), Kodak introduced an acetate safety film in 1908, but continued to produce cellulose nitrates until 1951. I can’t speak for other manufacturers, though, but this seems to defy common sense!