_Black Stains_ upon the hands, caused by nitrate of silver, may be removed by moistening them and rubbing with a lump of cyanuret of potassium. This salt is poisonous, if used to a great extent [_See page 139_]. Another safer, but more expensive plan, however, is to take a saturated solution of iodide of potassium in water, and then wash with nitric acid diluted with two parts water. _Stains upon White Linen_ can be removed by washing with a saturated solution of iodide of potassium containing a little iodine; then wash with water, and soak in a saturated solution of hyposulphite of soda until the yellow iodide of silver is dissolved. _The hands_ should always be washed after fixing a positive or negative picture, before again touching a glass to be coated, or the dipper; this precaution is necessary, lest any of the iron salt, or the hyposulphite, should get into the silvering solution and spoil it. _In taking Collodion Pictures_, it is always advisable for the sitter to be arranged before the glass is taken from the bath: this will save time and there will be less liability of the collodion drying. _A Good Negative_ may be known by its possessing the following characteristics:--By transmitted light the figure is bright, and appears to stand out from the glass; the dark shadows are clear, without any misty deposit of metallic silver; the high lights black almost to complete opacity. _A Glass Coated with Collodion_, if kept too long before immersion in the bath, will not be equally sensitive over its surface; the parts most dry being the least sensitive. _Glass Pans, for Scales_, can be procured by every one at trifling expense: Take a watch crystal, and place in the common metal pan; balance this with lead, or any weight: this can easily be kept clean, and is the most advisable for weighing all deliquescent salts, and chemicals employed in the collodion process. _Caution._--Persons engaged in making collodion, and using ether and alcohol, must bear in mind that these chemicals are _very inflammable_; hence extreme caution is necessary to avoid exposing them to the flame of a lamp or candle. I have known of several serious accidents, of recent date, all of which were caused by the imprudence of the experimenter in the particular above mentioned. _Wipe the Plate-holder_ every time before the glass is put into it: this will prevent spots, which might otherwise occur from the presence of nitrate of silver solution which drained from the plate previously used. These spots are of an opaque yellowish tinge, and in shape resemble the stain which would be occasioned by a _splash_ of water.