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A little different kind of gilding is carried out in Slokas 602-603. (See Footnote 23.) Expressed juice of the leaves of Rudanti (Cresa Cretica) embedded in liquid gold and admixed with copper, is to be smeared on copperleaves which are to be then roasted in Puta by one who is endowed with good fortune. Thus smeared and roasted three times, copper can be turned into gold. (602, line 2, and 603) 24 This is the process Needham' names as "Surfacelayer enrichment by withdrawal" of the base metal. Either an alloy of the noble metal or that of other metals with a layer of nobel-metal alloy on the surface is used in this method. When heated, the base-metal from the surface layer is oxidised and removed usually with the help of an acid. The noble-metal remains unchanged and this leaves its layer on the surface of the alloy. In the above-mentioned ' Sloka, copper is first coated with copper-gold alloy and subsequent heating causes copper to form copper oxides which are dissolved in organic acids, whereas gold remains FN. 23 continued 24, | mardayet gulvake sriman gulvapatrani lepayet | lepanca putapakanca tribhistatkana ke bhavet || 603 || Needham, Joseph (1), Vol. 5, Pt. II, p. 250.

84 unchanged and gilding is thus achieved. The plant Rudanti (Cressa Cretica) provides the organic acid required in the process.