How the adventurer obtained his wealth remains a secret. He could not have made it all by the sale of his _elixir vitæ_ in Germany, though no doubt some portion of it was derived from that source. Voltaire positively says he was in the pay of foreign governments; and in his letter to the King of Prussia, dated the 5th of April 1758, says that he was initiated in all the secrets of Choiseul, Kaunitz, and Pitt. Of what use he could be to any of those ministers, and to Choiseul especially, is a mystery of mysteries.
There appears no doubt that he possessed the secret of removing spots from diamonds; and in all probability he gained considerable sums by buying at inferior prices such as had flaws in them, and afterwards disposing of them at a profit of cent per cent. Madame du Hausset relates the following anecdote on this particular: "The king," says she, "ordered a middling-sized diamond, which had a flaw in it, to be brought to him. After having it weighed, his majesty said to the count, 'The value of this diamond as it is, and with the flaw in it, is six thousand livres; without the flaw, it would be worth at least ten thousand. Will you undertake to make me a gainer of four thousand livres?' St. Germain examined it very attentively, and said, 'It is possible; it may be done. I will bring it you again in a month.' At the time appointed the count brought back the diamond without a spot, and gave it to the king. It was wrapped in a cloth of amianthos, which he took off. The king had it weighed immediately, and found it very little diminished. His majesty then sent it to his jeweller by M. de Gontant, without telling him of any thing that had passed. The jeweller gave nine thousand six hundred livres for it. The king, however, sent for the diamond back again, and said he would keep it as a curiosity. He could not overcome his surprise, and said M. de St. Germain must be worth millions, especially if he possessed the secret of making large diamonds out of small ones. The count neither said that he could or could not, but positively asserted that he knew how to make pearls grow, and give them the finest water. The king paid him great attention, and so did Madame du Pompadour. M. du Quesnoy once said that St. Germain was a quack, but the king reprimanded him. In fact, his majesty appears infatuated by him, and sometimes talks of him as if his descent were illustrious."