Lucky is the man who can always make the slide he wants. Oftentimes a slide comes out of the fixing-bath a little too dense or just a trifle thin, or maybe there is just one corner too dense, which spoils the whole. In such cases a reducing-bath must be resorted to.
First we will take in hand slides that are heavy, dense, or over-developed either in whole or part.
The Howard-Farmer reducer is a standard one for this purpose—it is well known and is generally satisfactory :
Hyposulphite of soda i ounce.
Water ... 10 ounces.
Saturated solution of fenicyanide of potassium.
These should be mixed only for immediate use. Take 2 ounces of No. i and io drops of No. 2.
Soak the slide to be reduced and place it in the solution, watch it carefully and take it out before the full reduction you require is reached, and wash well at once. If only partial reduction is required use a soft camel-hair brush, and apply the solution to the parts required. The solution may be used stronger or weaker as the density of the slide requires.
This reducer acts more quickly upon the high lights and half-tones than upon the dense portions, and it must be carefully watched on this account. If the dense portions require acting upon most, as is generally the case, the Persulphate of Ammonia Reducer should be used, as it attacks the dense portions first and other parts later. For particulars of its composition and use see p. 36.
Take the slide and place it in a clean dish, and flow over it of the following sufficient to cover the plate well:—
Mercury perchloride ... 2 drachms Ammonium chloride 1 drachm.
Water to make . . . .10 ounces.
This can be used repeatedly.
When the slide has assumed a white appearance take it out and wash it well for five minutes ; now take another dish and place the slide in it, and flood over it a solution of liq. ammonia -88o 1 part in 10 parts water. This will at once darken the slide and make it much denser. Other methods of Intensification identical with those given in negative-making may be found in the chapter under that heading.
There are many points in the practice of lantern-slide making that have only been briefly touched upon on account of space, but the slide-maker will have had given him sufficient to indicate a' course of work and study ; every earnest slide-maker finds out ways and means of his own as his practice extends, and it is such matters arising out of experience that go. to make up our successes.