7. Since then we have briefly set forth what can be done with the teachings which they suppose to be secret, we have [Sidenote: p. 105.] displayed their easy system according to Gnosis.[136] Nor do we wish to keep silence as to this necessary point, that is, how they unseal letters and again restore them with the same seals (apparently intact). Melting pitch, resin, sulphur and also bitumen in equal parts, and moulding it into the form of a seal impression, they keep it by them. But when the opportunity for unsealing a letter[137] arrives, they moisten the tongue with oil, lick the seal, and warming the drug before a slow fire press the seal upon it and leave it there until it is altogether set, when they use it after the manner of a signet. But they say also that wax with pine resin has the same effect and so also 2 parts of mastic with 1 of bitumen. And sulphur alone does fairly well and powdered gypsum diluted with water and gum.[138] This certainly does most beautifully for sealing molten lead. And the effect of [Sidenote: p. 106.] Tyrrhenian wax and shavings of resin and pitch, bitumen, mastic and powdered marble in equal parts all melted together, is better than that of the other (compounds) of which I have spoken, but that of the gypsum is no worse. Thus then they undertake to break the seals when seeking to learn what is written within them. These contrivances I shrank from setting out in the book,[139] seeing that some ill-doer taking hints from them[140] might attempt (to practise) them. But now the care of many young men capable of salvation has persuaded me to teach and declare them for the sake of protection (against them). For as one person will use them for the teaching of evil, so another by learning them will be protected (against them) and the very magicians, corruptors of life as they are, will be ashamed to practise the art. But learning that the same (tricks) have been taught beforehand, they will perhaps be hindered in their perverse foolishness. In order, however, that the seal may not be broken in this way, let any one seal with swine’s fat and mix hairs with the wax.[141]