I mixed 'liquid metal' (which is a 2 part epoxy resin) with a touch of black boot polish ..It worked well for a minor repair...I would think you could try Araldite as a substitute for the resin I used.... I'd advise mixing up a small amount and doing a 'test' repair in a scrap switch, dynamo end cover or similar first...Ian
A friend from the old job restored Bakelite phones part time then full time upon retiring
He repaired stuff for me using what he described as a super glue mixed with fabric dye
When the surfaces meet without the blackening agent - white glue lines would appear, the blackening although slightly visible could be finished until not visible by polishing or surface finishing