| Show the blaking of mirrors thoro there are arc three kinds of mirrors known to commerce t the lie french plate tho the german plate and tho the common american glass usually called I 1 shocks tho latter can be told to ld by their tendency to plant the noso nose well around toward the ear car or a more or less successful effort to ret get both eyes in the same place the german plate is imported in regular sizes already silvered it is a very thin but generally perfect glass and comes about one fifth ell cheaper per than the french plate which is used altogether for first class mirrors the difference can bo be told by pressing the finger on the face of the glass by which the thic thickness kriess can readily be perceived tile there are three factories in tho the united states manufacturing plate glass but none of them has yet succeeded in securing tho the necessary whiteness and freedom from bubbles imperfections that are not noticeable in clear plate become very prominent when silvered silvering quality glass as it is known is carefully selected by the french manufacturers and sold for that purpose commanding a higher price than the balance of the product there are two different processes of silvering mercury being used for one and nitrate of silver for the other the latter are known as patent backs although not patented and are generally replacing mercury on account of the greatly decreased risk in handling in the former process a sheet of tinfoil somewhat larger than the mirror wanted is placed upon a level table tho the bed of which is of glass or marble and which must be absolutely clean and free from even the slightest scratch strips of glass are then placed on tho the edges of the foil to prevent the mercury from running off As much mercury as the inclosure will hold is then poured over the foil after which the plate is floated on and entirely covered with heavy iron weights the table is then tilted and the surplus mercury drains off after which they are stood on edge to dry which requires from ono one to two weeks in making a patent back the glass is ia laid on oil a table underneath which is a steam coil the nitrate of silver in solution is then poured bri on a gentle heat beat applied and the silver precipitated the back is then painted and the mirror is complete either process requires a great amount of skill and care absolute cleanliness is imperatively necessary in in every part of the work distilled water is used in cleaning the plate preparatory to silvering and a drop of perspiration or dust spoils the work ork globe democrat |
