This week i learned how to process them - without any fancy equipment.
Let's start at the end with the outcome. This is a negative i have processed. It is a picture of Blanche Edmonstone at Dubbo Park, 1919. The photo was taken by her sister, Victoria Edmonstone, with a Box Brownie 2, using Kodak 125 film.
Here are enlargements of the face (a 1/2" by 1/2" area on the negative). The first shows a focus on the surface scratches, which are then dealt with in post processing (potentially a great deal of work).
The second enlargement shows a focus just beyond the surface - giving the entire image a slight blur and removing most small scratch marks.