CERTINAL A highly concentrated liquid developer in one solution form, introduced by Ilford Ltd., March, 1909. The best proportion for developing plates and films which have received normal exposure is certinal 24 drops, water i oz. At a tempera ture of 6o° F. (nearly 16° C.) the image appears in a few seconds, and development will be com plete in from 4 to 8 minutes, according to the plate and the class of negative desired. The rapid appearance on dry plates must not be mis taken for signs of over-exposure, and the image will need to be developed for density. As a rule, the image on a properly exposed plate appears in 15 seconds, and development is complete in 6 minutes. With under-exposure the best results are obtained by using the developer weaker (16 drops of certinal to each ounce of water) and developing longer. Over-exposed plates need a stronger developer and the addition of potassium bromide (certinal 48 drops, water i oz., io per cent. solution of bromide 48 drops) ;
development will then take about one-fourth less time than would be required when exposure and developer are normal. For tank or stand development oz. (izo drops) of certinal should be added to 25 oz. of water ; development will be complete in from 3o to 6o minutes, according to temperature, plate, subject, and type of negative desired. For lantern plates and bromide paper the best strength is 16 drops to each ounce of water, but gaslight papers and plates need double that strength. More con trast may be obtained on papers and lantern plates by using a stronger developer, and still more by adding potassium bromide, while softer results are obtained by diluting the developer. Additional bromide gives warmer blacks, especi ally on gaslight papers and plates.