This little clip shows fixing a tintype I made of Steve Jelf in his 1915 runabout. I shot the image off the computer screen. Development brings out a negative image and fixing in potassium cyanide converts the negative image into a positive image in a matter of seconds. This process was invented in the early 1850s and continued until the model T era.

https://m.youtube.com/watch?feature=youtu.be&v=xN5S6HYx668

Man, that conversion WAS fast!
The first of the fluid is hitting the negative on the left and bam, that section is changing.
Are there any extreme procedures when working with the potassium cyanide? Yikes.

Well, you don't lick your fingers after using it. And ... the addition of acids create cyanide gas, so .... keep any acids away at all costs. Cyanide was the preferred fixing agent because it's so aggressive. It also washes off the plate very fast.

A past made from cyanide, silver nitrate and chalk can be used to replate silver without electricity. You simply rub it onto objects made of copper or brass.