I have usually preferred Mr. Archer's collodion, as the most certain and cleanest. The silver bath is composed of thirty grains nitrate of silver and two drops of nitric acid to each ounce of distilled water. An even film may be obtained by the following means:--Represent the plate of glass by the following figure: +--------------------+ | 1 3 | | | | | | 2 4 | +--------------------+ Hold the plate with the left hand at 1, pour a body of collodion in the centre: tilt towards 1 (being careful not to let it touch the thumb), incline towards 2, run into 3, and pour off at 4: then hold the plate vertically (resting the corner 4 on the neck of the collodion bottle) to drain: incline it first to the right and then to the left, repeating this several times until the ridges are removed. By these means an even film may be produced, without a thick ridge, from 2 to 4. The time it may be left before plunging into the silver bath will depend on the temperature (about half a minute). Dip evenly into the bath, lifting up and down to allow of the evaporation of the ether: the film will also saturate more rapidly. When the greasy appearance is gone, it is ready for the camera. Sometimes the film is nearly transparent and bluish, not having sufficient iodide of silver; or it may contain too much iodide, the greater part flaking off in the bath, leaving the collodion with very little, and that patchy; or from being placed in the bath too quick, the lower corner still present a reticulated appearance, which of course renders it useless. Having exposed the plate the necessary time, the next step is the development. The solution I usually employ is prepared with protosulphate of iron. I do not find distilled water absolutely necessary (during the summer months I fancied the tones were improved by using ordinary water, perhaps from containing a little lime), and the acetate acid is not glacial, but a description termed Beaufoy's, much less expensive. The proportions are-- Water 2 ounces. Acetic acid 1 drachm. Protosulphate of iron 8 grains. Nitric acid 2 drops.