The Heliotype Process

One of the most important discoveries oí modern timea is n rncthod of produoiilg fac-8Ímilee of choioe engrayiñgs, iviiiitiii:':;, Örnwings, etc.; ealled the " boliolypi' process." The. discovety dr inventioii of tho process mny lo said to have been mitclc in 1855, though it is only very rerently that it líos beeu bronght'to it present high degree of p'éïïecliöu. Brictiy stated, the prooess is ns folldws : (iclatijH1, mixed with biühromate of po'ash, Iuiü the property ut' being so rtüted upon by light tliat its pores beciiwe entirely, )iirtinlly ot not at all uloscil, acyordiug to the amownt of light. By mixing ftlum with this bicbromnted gejatine, and drying it on ptates in the dixik by artificial heat, a porohment-like slieet ír prodnqecl liard enough to print from ; and by exposing this sheet to light throngh a photoferaphiö negiitive, its surfaoe beoomes so vari:(! as exuctly to reproduce the marks of the engraver and etchor. A 'tor the píate lias been prepared, it is printed i from in au ordiuary press, oopiea being tlms produced very rnpiclly, and, of eonrsi!, chéaply. So perfectly is the original reproduced, that only an experienoed eyo ivill readily dêtect the diñerence. Copies ol One si; ( 1 engravings, and other high-prieed pictures are thus bronght witlün reftch of peoplo of limited meaiis ; and the, method by which the pieture is produced, being parely mechanical, insures ft mueh more perfect copy than any lithographic process enn prod'iiee.