Silver halide is sensitized by adding thiosulfate at 1 - 100 grams / mole of silver present. Unfortunately, this level is based on grain size (surface area actually) and therefore unless you have electron micrographs you have to determine it by trial and error.
Gold is used a 1 part of gold salt / 3 parts of thiosulfate.
Don't use Dichromate.
As a very kind person has noted, this post should read Thiosulfate is added at the rate of 1 - 100 mg / mole of Silver present. And it is based on Sodkum Thiosulfate Pentahydrate.