If you have a Doomfold tier jeweller, you can make a Refined Black Adamant once a day (18 hour cooldown). You automatically get the recipe. It uses only a single Black Adamant.
It takes 3 (!) Refined Black Adamants to craft a single piece of level 115 jewellery, so it takes 3 weeks for a jeweller to make enough for 7 pieces. Of course, not everyone will want 7 pieces of crafted jewellery, but you get the picture, they are in demand. They have been selling for 20-30g each.
Because you can level a jeweller by polishing gems, and gems are easily available for most tiers, even a low level character can become a Doomfold jeweller. You don't need mastery to craft the Refined Black Adamant, so you only need proficiency in the lower tiers. I have lots of emeralds and zircons if you need some to polish. Green garnets (Westfold tier) and red agates (Eastemnet tier) are usually the bottleneck for levelling.
If you have or can get a Doomfold jeweller, you should make a Refined Black Adamant every day, either for yourself or friends or to make some gold. Black Adamants are easy to get, so if you want a bunch, let me know.