♦Slate♦
Slate-paper, which takes its name from the fact that it can be cleansed like a slate, is prepared from the regular product, of the required thickness and consistency, by the use of benzine, followed by a preparation made of lead, zinc oxide, turpentine, seed-oil, copal, and sandarach.
Soft plate-paper is a thick unsized paper, especially adapted to receive impressions for fine engravings printed from steel and other plates.
♦Filter♦
Filtering-paper, much used by chemists and druggists, is simply unsized open or porous paper. With such paper, of course, the process of manufacture ceases at the first drying or crushing rollers, all the finishing or hardening operations being omitted.
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♦Waterproof♦
Waterproof papers comprise a large and most useful class. It is practically only within the past twenty-five years that a process has been known and employed for rendering a paper waterproof by destroying its absorptive properties. At the present time there are many and various methods used in waterproofing, such as soaking the stock in dissolved shellac and borax. This method is found especially satisfactory in waterproofing heavy paper and boards. Another process is by brushing the surface of the paper with boiled oil, and paper thus prepared was formerly used largely in lieu of bladders and gut-skins for wrapping butter, covering fruit-jars, etc., but it has been almost entirely superseded by the introduction of parchment-paper, of which mention will be made later.
♦Paraffin♦