Johan Isaac Hollandus (late sixteenth Century) is said to have been the two Isaacs Hollandus, father and son, Dutch adepts, who wrote De Triplici Ordinari Exiliris et Lapidis Theoria, Mineralia Opera Sue de Lapide Philosophico and other works on Alchemy. The details of their operations on metals may be the most explicit that have been given in writing, and may have been dismissed by some because of this very clarity. John Read, a Professor of Chemistry, in his Prelude to Chemistry, an Outline of Alchemy, dismisses the writing of the Hollandus pair in a few words, possibly because their clarity of detail led him to suspect a ruse. 

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The Hand of the Philosophers

This is the Hand of the Philosophers with their dear secret signs, with which the old sages united with each other and took oaths. Nobody can understand this Hand with its secret signs, unless he becomes first a juror of the philosophers, (one who swore loyalty to a philosopher), and has loyally served them in the Art Alchemia. Consequently, those who have not this Hand and do not understand its secret signs, nor have taken the oath of loyalty, are bastards in this Art. They do not possess the philosopher’s treasure. That is why I advise all those who do not possess the secrets of the Hand not to start working in the Alchemical Art, nor to believe books or writings, since they will all only be cheated in the secrets of the Hand. Therefore, everybody had better be careful.

In this Hand is locked the secret of the philosophers, that is, of the seed and the earth, as will be told later.