“He found a new way to print with a single press, at the same time, any human figure, and flowers, and every other thing in various colours”, reports an eighteenth-century source concerning one of the more incredible inventions of the Prince of Sansevero – the simultaneous printing of more than one colour, a largely unknown typographic technique at the time. Having designed and installed some printing presses in his home in Piazza San Domenico, di Sangro managed to print in polychrome, and in one go, not only figures, but also beautiful characters.

Among those able to admire his prints and his polychrome printing was also the Frenchman de Lalande, who described them as follows: “the art of printing in several colours is another of the things which the Prince perfected. He showed me what he had printed on paper and white silk, where he had printed a number of flowers in different colours, with one plate and one turn of the press […] I don’t think that the tables made in Paris by M. Gauthier were realised using the same advantageous procedure”.

What everyone can still appreciate is, however, the result of the system with which the Prince succeeded in printing polychrome characters. “The monument of the new surprising invention” – as Lorenzo Giustiniani rightly defined it in his Historical-critical essay on typography in the Kingdom of Naples (1793) – is in fact the title page of the original edition of the Lettera Apologetica, with the characters in black, red, green and orange. It was di Sangro himself who underlined the extraordinariness of his own method, which caused at least as much amazement as the unorthodox contents of his literary masterpiece: “The difficulty of this invention is clear to those expert in the art, and is generally considered insuperable by all; as is the benefit which can come from it”.