1155. Another Method Of Making Light Filters

Another Method Of Making Light Filters. Use a 10 per cent. solution of gelatin instead of the distilled water given in the filter dye-bath of the first method. The following are the quantities of gelatin solution necessary for the given quantities of dye solutions:

The gelatin and dye solutions must be thoroughly mixed together.

1156. The method of coating plates with this pre-dyed gelatin will be the same as with the plain gelatin; but it will be seen that the absorption of the filters made by this method will depend upon the amount of gelatin solution which is coated onto the plates. Thick and thin coatings may be made, and the most suitable pairs of plates selected, by testing after they are dry.

1157. Color Sensitizing Of Plates

Color Sensitizing Of Plates. Although there are several brands of color sensitive plates on the market, a description of the method of home sensitizing will be useful to the enthusiastic three-color worker. In selecting a stock-manufactured dry plate for the purpose of making the same color sensitive, the first consideration must be that the plate must develop with a minimum of chemical fog. There may be many makes of American plates eminently suitable from this point of view, but the only one the writer has had the opportunity of thoroughly testing is the Seed No. 26, which, with care, gives excellent results. Seed Gilt Edge was not found so satisfactory for the purpose.

1158. The Sensitizers

The Sensitizers. The scientific principles involved in sensitometry are quite outside the province of this article, it being proposed only to deal with a practical method of making it possible to make ordinary dry plates sensitive to all the colors of the visible spectrum.

1159. In the first place the following dyes must be procured:

1161. Before commencing to bathe the plates, suitable provision must be made for drying them. For this purpose employ cither a drying cupboard, through which a current of air is passed, or one in which a quantity of calcium chloride or quicklime is placed in a dish. A current of warm air is the best means of drying.

1162. The ordinary red light of the dark-room may be used for the preliminary preparations. Well wash and dry a flat porcelain dish, large enough to hold two or three plates more than it is proposed to sensitize at one time. Into this lay the plates, after carefully dusting. Now, tilt the dish so that the empty end is down, and into this pour the sensitizing dye-bath; then tilt the dish back so that the solution flows in one sweep over the plates.

1163. Immediately it is seen that the plates are covered with solution; put out the red light, and proceed, in total darkness, to gently rock the dish, in order that the dye may act equally upon each of the plates in it. Bathe for five minutes and then stand the plates in a draining rack, and put them into a cupboard or dark box to drain while other plates are being bathed.

1164. As these plates are now panchromatic, no red light must be used with them after they have once been wet with the dye solution; but a deep green light, if carefully tested for safety, may with caution be employed. After the plates are dry, they should be backed with a mixture of vegetable black and dextrine. No red backing must be used.

1166. In either case a proportion of Methyl Alcohol may be added to assist the drying, making a similar reduction in the amount of water used.

1167. The plates may be bathed in alcohol after they have been allowed to drain for half an hour. Two alcohol baths should be used, allowing the plate to stay five minutes in the first, and then transferring to the cleaner bath for two minutes. The surface of the plate may then be carefully wiped with a piece of soft, well-washed muslin. This will help to avoid markings which may otherwise occur. These plates should also be "backed" with black backing.