van Monckhoven, Désiré van. A Popular Treatise on Photography. Translated By W.H. Thornthwaite. London, 1863.
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As the preparation of photographic collodion requires a considerable degree of nicety in the operations of measuring and weighing, it will not be out of place here to make a few remarks relative thereto that may be. of some utility to the practical photographer.
Liquids are measured in glass vessels graduated into
ounces, drachms, and minims, the indicating signs and relative quantities of which are shown
in the following table:
1 pint contains 20 ounces xx.
j, or 1 ounce contains 8 drachms, viij.
j, or 1 drachm, contains 60 minims.
|Fig. 19.||Divided Measuring Glasses.|
Three of these graduated glasses will be found necessary-one of the shape Fig. 19, to hold 1 pint, and divided into ounces; another of the same shape, to contain 2 ozs. and divided into drachms, and a small measure, of the form of Fig. 20, holding 2 drachms and graduated into minims. When used for measuring liquids, they should be held horizontally, on a level with the eye, and the fluid poured in until its surface reaches the line corresponding with the required figure on the glass. As these graduated glasses have lines corresponding with each other both at the front and back, the proper position of the measure as regards its level is easily shown.
Fig. 21. Table Balance.
The table balance, Fig. 21, will be found the most convenient form for weighing quantities up to 2 lbs. It should have a set of weights from ½ oz. to 2 lbs.
22. Hand Scales
For weighing smaller quantities, the hand scales, Fig. 22, is required. The pans should be made of glass, and there should be a suitable set of weights, from ½ grain to 2 drachms. Glass is the best material for the scale-pans; but if formed of metal, it will be requisite, before proceeding to weigh any chemical, to place a piece of rag, paper of equal dimensions in each pan, by which arrangement the whole of the substance is conveniently removed after weighing, and any injurious action avoided. When fluids are required to be weighed, glass or other vessel to hold the liquid, is first accurately balanced or counterpoised, and then the weighing done in the ordinary manner.
The preparation of Iodised Collodion requires the following substances:
|Ether, sp. gr. .720||3 ounces.|
|Alcohol, sp. gr. .805||½ ounces|
|Iodide of Cadmium in powder||18 grains.|
|Bromide of Cadmium in powder||6 grains.|
The gun-cotton is first put into a suitable glass bottle; afterwards the iodide and bromide of cadmium and the alcohol. The mixture is then strongly agitated to dissolve the salts of cadmium, and to open the fibres o1 the cotton, and facilitate its subsequent solution. The ether is now added, and the whole again well shaken until the cotton is dissolved, when the bottle is closed with a good cork and left to settle for twenty-four hours, after which the clear and limpid portion is decanted into small glass bottles for use.
From the circumstance that collodion containing the iodiser as above is liable to decompose, it will generally be found preferable to prepare the collodion and iodising solution separately in the following manner.
Plain thick Collodion, without iodides or bromides, is first prepared as follows:
Into a bottle of about one quart capacity is placed
These materials are very strongly agitated together, and left to settle for some days.
A solution of iodide and bromide is also prepare, thus:
|Iodide of Cadmium||154 grains.|
|Bromide of Cadmium||54 grains,|
The iodide and bromide of cadmium should be ground very fine in a porcelain or glass mortar with a small quantity of the alcohol, then the remainder added, and when the salts are dissolved, the whole carefully filtered. The clear solution must be preserved in a well-stopped bottle.
To prepare Sensitised Collodion, pour into a four-ounce bottle
|Thick Collodion (No. 1.)||1 ounce.|
|Solution of Iodide and Bromide (No. 2.)||3 drachms.|
Immediately after the bottle has been -,veil shaken, so as properly to mix the ingredients, the sensitised or iodised collodion is ready for use, but is improved by being kept a few hours after sensitising before being applied.
Both the plain collodion and the alcoholic solution of iodide and bromide of cadmium can be preserved for any length of time without deterioration, provided they are kept separate and in well-closed bottles; and the sensitised collodion can, therefore, be prepared when required with great facility.
The formula for sensitised collodion just given will be found to work 'nest at a mean temperature of 60° Fahr. When the weather is very hot a little more alcohol. must be added, and the quantity of ether slightly diminished; and, on the contrary, when the atmosphere is very cold the alcohol may be diminished, and the ether increased.
When a glass plate is coated with collodion , a larger quantity is poured over its surface than is really required, the surplus being received in a bottle; it will therefore be easily understood that after a considerable number of plates have been coated, the proper relative proportions of the constituents of the collodion will have been disturbed by evaporation, and that both ether and alcohol must be added to bring it to its normal condition. It must be borne in mind in making the required addition of ether and alcohol, that ether being much more volatile than alcohol., a larger relative proportion will have evaporated, and consequently a larger quantity of ether must be used than of alcohol.
If the layer of collodion on the glass appears too thin, a little of the thick collodion, No. 1, must be added; if, on the contrary, it be too thick, and in consequence does not spread evenly over the glass, it can be diluted with a small quantity of a mixture of two parts of ether and one of alcohol.
If the collodion film detaches itself from the glass plate after being sensitised in the silver bath, it indicates that a larger proportion of ether is required, or that tile guncotton employed is not suitable, in which case recourse may be had to a gun-cotton prepared according to the formula given in Note 3, which produces a very adhesive collodion, especially applicable when glasses of large dimensions are employed.
If too much alcohol be added to the collodion, the film is liable to become detached, and the coating itself has a wavy uneven appearance. if there be too much ether the layer is very adhesive, but it is difficult to get the collodion to spread itself evenly over the plate, especially if it be of any large size.
Collodion ought to be preserved in well-stopped bottles, but it is indifferent whether bottles with glass stoppers or furnished with good corks be employed; they ought, however, as much as possible, to be kept quite full, and in the dark.
Iodised collodion is never good the first day of its preparation; it must be kept for at least two days to acquire all its properties; neither must it be kept too long, for impression. 3 are then taken with it less rapidly.
Collodion is very unstable; sometimes without any apparent reason it becomes slow in producing impressions; at other times it changes to a red colour at the end of a few days. In this latter case recourse ought to be had to a new preparation, and care taken to ascertain if the materials previously employed were sufficiently pure. The colour of good collodion is commonly of a very light lemon colour, although sometimes completely colourless.
A very clear and perfectly settled collodion must always be made use of. The following is an excellent little apparatus for pouring out collodion free from sediment.
Fig. 23. Glass apparatus for decanting Collodion.
A very tall and narrow bottle must be procured of the form indicated by Fig. 23. The cork a is pierced with two holes made with a round file; two small glass tubes are fitted to it, of which A goes a little way through the cork, and the other is bent down in the form of , only one branch is shorter than the other. The longer branch is dipped into the collodion at a short distance from the bottom. After a certain quantity of collodion has been used for several hours, what remains should be poured into the bottle by lifting the cork a, which must. be again replaced. The next morning the collodion will be perfectly settled, and by blowing into the tube A, the clear liquid passes by the tube D a B, from the extremity of which it is received into a proper bottle.
Care must be taken that the surface of the collodion be lower than the extremity of the tube B; should it be otherwise the tube must be raised by causing it to pass through the cork, or else the collodion would continue to flow after the required quantity had been decanted.