hograph

ve Details-Scraper-Tympan-Practi

an interesting fact which either reflects much credit upon the ingenuity of the early lithographic printers or points to an unreasonable conservatism on the part of the present-day craftsmen. A discussion of this

xtent these requirements are fulfilled b

ticism. In fact, its general mechanical arrangements are so exceedingly simp

D (Fig. 8) is both effective and necessary, owing to the

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tympan C, is sufficiently elastic to ensure the closest possible contact. Figs. 6 and 7 show one or two constructive details b

mpression. The shaft H runs across the press and operates a similar cam to E on the opposite side. These tw

not a little attention and intelligent manipulation. It is practically impossible to s

. 6

e back of the tympan is usually dressed with a mixture of tallow and plumbago, a dressing which requires frequent renewal. The plumbago possesses but little body, and its salutary effect soon passes away. To prevent this and to increase its adhesiveness it is sometimes

unwise to pull a number of impressions from small stones with a large tympan, for if this practice is persisted in the tympan

ood scrapers of different sizes. The "dents" produced by a s

the risk of breakages. In fact, the pressure is frequently so keen and of such a direct character as to render this arrangement little short of a neces

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rk are of sufficient importance to warrant a full description