To start with, the fluoride salt of silver is too soluable to make a good imaging material and that is why it has not been used. It would be slower than chloride, if it could be used, I suspect, and the sensitivity would be in the UV range of the spectrum.

Silver chloride is the most developable and quite fast, but mainly in the UV region. Silver bromide is faster but in the visible (blue) region, and tends to give lower contrast images. Part of this is due to the excess bromide present in the emulsion. If you take a washed and unwashed emulsion, and compare them (bromide) you see a higher contrast with the washed emulsion in most cases due to the lower amount of excess bromide.

Iodide, up to about 10% is quite useful in many emulsions such as bromide or chloride, but the usual value is from 0.3% - 2% in most cases. Distribution of iodide in the grain is also important.

A pure iodide crystal, as such, cannot be developed by ordinary developers. Too much restraint from the iodide and most developers are too low in activity. But, if you force them, they develop to yield a high speed image with near ortho sensitivity. Pure iodide emulsions are orange red in color and have near ortho sensitivity built right in to them. That is one reason why a pure Br/I emulsion gains speed with added Iodide (among other reasons) is the broadening of the spectral sensitivity imparted by iodide.

Hope this helps.


You have a very good point. Having seen some horrible lab accidents even by trained chemists, you are giving some good advice here. Anyone without chemical training, who does 'research' or 'development' has to assume a very large risk factor for themselves and their families.