From the Memoirs of Jacques Casanova:
The most enjoyable dinner I had was with Madame de Gergi, who
came with the famous adventurer, known by the name of the Count de
St. Germain. This individual, instead of eating, talked from the
beginning of the meal to the end, and I followed his example in one
respect as I did not eat, but listened to him with the greatest
attention. It may safely be said that as a conversationalist he was
unequalled.
St. Germain gave himself out for a marvel and always aimed at
exciting amazement, which he often succeeded in doing. He was
scholar, linguist, musician, and chemist, good-looking, and a
perfect ladies’ man. For awhile he gave them paints and
cosmetics; he flattered them, not that he would make them young
again (which he modestly confessed was beyond him) but that their
beauty would be preserved by means of a wash which, he said, cost
him a lot of money, but which he gave away freely.
He had contrived to gain the favour of Madame de Pompadour, who
had spoken about him to the king, for whom he had made a
laboratory, in which the monarch—a martyr to
boredom—tried to find a little pleasure or distraction, at
all events, by making dyes. The king had given him a suite of rooms
at Chambord, and a hundred thousand francs for the construction of
a laboratory, and according to St. Germain the dyes discovered by
the king would have a materially beneficial influence on the
quality of French fabrics.
This extraordinary man, intended by nature to be the king of
impostors and quacks, would say in an easy, assured manner that he
was three hundred years old, that he knew the secret of the
Universal Medicine, that he possessed a mastery over nature, that
he could melt diamonds, professing himself capable of forming, out
of ten or twelve small diamonds, one large one of the finest water
without any loss of weight. All this, he said, was a mere trifle to
him. Notwithstanding his boastings, his bare-faced lies, and his
manifold eccentricities, I cannot say I thought him offensive. In
spite of my knowledge of what he was and in spite of my own
feelings, I thought him an astonishing man as he was always
astonishing me. I shall have something more to say of this
character further on.
When Madame d’Urfe had introduced me to all her friends, I
told her that I would dine with her whenever she wished, but that
with the exception of her relations and St. Germain, whose wild
talk amused me, I should prefer her to invite no company. St.
Germain often dined with the best society in the capital, but he
never ate anything, saying that he was kept alive by mysterious
food known only to himself. One soon got used to his
eccentricities, but not to his wonderful flow of words which made
him the soul of whatever company he was in.
Saint-Germain also dispensed an "elixir of life," which Doug Skinner of Fortean Times describes as "a tea of elder flowers, fennel, and senna pods, soaked in spirits of
wine. I’m afraid it was a laxative – a potent one, in fact."