We don't have synonyms for tinkal yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are tindal, tincal and tikal.
(n) :
Alternative form of tincal (“crude borax”). [(chemistry, dated) crude native borax, formerly imported from Tibet, and once the chief source of boric compounds]
(n) :
Alternative form of tincal (“crude borax”). [(chemistry, dated) crude native borax, formerly imported from Tibet, and once the chief source of boric compounds]