You ask them to consider paying you in actual gemstones rather than money made from them.
6*
The dwarves
snicker amongst each other, or so you believe, and their leader nods. "This is agreed! Gemstones for tax, this is very good indeed. We bid you farewell." You then send envoys to King Salus to update him on situation and have the details eked out.
978 AD, Autumn
You wish your children good night and then leave your wife in her chambers as you go read a book on military conquests of the Kings of Dahnia from early 10th century.
Then there's an explosion so loud and so powerful that you fall off your chair. Guards are yelling, maids are screaming and people are running everywhere.
The tower of the royal alchemist lost its roof and is on fire!
The next morning, the body of the alchemist is recovered and his students bemoan his death.
"He was tinkering about the Fireblood substance for years, yet he had no luck with finding the exact formula. And the luck has only worsened, now that he died from his foolish research!" You think about it for a moment.
A) Clearly, Fireblood must be something truly precise and highly complex. Let's forbid its research, lest the whole of palace blows up on next mishap.
B) Truly, if he made such a big explosion with Fireblood components or similar substances, we might find some use for it! The students ought to continue their late master's studies!