It is best to mix cobalt with some fritted cullet in order to disperse it before charging. The depth of color produced by nickel depends on the character of the alkali in your cullet. Nickel oxide is very refractory and doesn't want to go into solution readily. You will need to melt your cullet at a higher temperature if it doesn't go into solution. We used it to create Schmaltz Glass back in Madison in the 60's Never touch silver nitrate with your hands or let it touch any part of your body.
Silver nitrate is also very expensive.
Should only be used with caution.