Blackening 9kt Yellow Gold: Best Methods & Alternatives

Question
I am a jeweller and I am trying to blacken a 9kt yellow gold ring using a torch, however it is not working very well.  Is there a better method?

Answer
Hello Karen,
though the torch  and the high copper  content of  9Kt gold  would make one think it  would be  easy to  coulour with heat treatment. It is not! A better product  can be found at most jewelers supply houses, Jax black for  gold is  a relatively safe compound to use and incurs no hazardous shipping charges associated  with it. Some recipes can  be found by searching the Orchid at ganoksin.com archives as there you'll get a wide range of experience from  jewelers around the globe, and  of varying  skill levels. But the best reference and  book of formulas is Harold O'Connor's "Jewelers Bench Reference"- though out of print it is available from  services like alibris, or abe books, or amazon periodically at  low  ( to  unbelievably high- and  not worth the expense!) rates for a book you'll refer to  almost daily  on anything  from formulation and equations in calculating  x quantity of metal to  the  different patina recipes and colouring  methods and  directions for  different metals.
If you want to experiment,  make tiles of  9Kt gold and various flame temperatures and  exposure times, write them down along with the ambient temp. of the studio or space you are in as  humidity and  other  factors  all contribute to  consistency particularly  when making  production pieces as opposed to one-off's of which the  results  may vary widely since you aren't trying to duplicate them. Nonetheless any commercial recipe  is better than torch firing as it not only weakens any easy soldered joins  and risks  a melt down  but  it is far easier to torch colour a traditional japanese alloy like shibuichi or shakudo that  have a very high  copper content and  only 4% gold ( shakudo) or a sterling  copper alloy (shibuichi). With shibuichi it is possible to get a range of greens, pinks, golds,blues etc. that can be  sealed with  micro-crystalline wax  to preserve the results. Any torch fired  colour  must be sealed with a wax of  some sort, the micro-crystalline waxes  being superior to any  shellacs or   enamels, etc. too. But  fluid colourants  do not  need to be sealed if applied according to  manufacturer's directions. there are  a number of  people that use peroxide as an oxidizer on gold  of lower karats, but I  use a formula that  O'connor  recommends or  some gun bluing, from any hardware when it is desired. Gun bluing is cheap and readily available and works well to  give  gold a deep rich  grey black or blue-black  colour that  doesn't  need  much treatment after applying.
I hope this helps you. Feel free to  contact me  if you  can't get the O'Connor book, which is my  highest recommendation ( he also  touches on  torch  colouring in it, as does Tim McCreight in the " Complete Metalsmith"). the Orchid forum should provide you with a wealth of  various recipes for  oxidizing  gold too.
Best Regards, Ari