Chromium intensifiers

Chromium Intensifier Chromium intensifier is a proportional intensifier the amount of intensification is proportional to the amount of silver present in the negative. Therefore, denser areas of the negative are affected more than thin areas. Chromium intensification is useful for increasing contrast since it has little effect on thin, shadow areas. To be effective, chromium intensification must often be repeated several times. 

The two main ingredients in chromium intensifier—potassium dichromate and hydrochloric acid—are both hazardous chemicals. Hydrochloric acid can burn a hole in your skin, and dichromate can cause serious skin irritation. Handle chromium intensifier with gloves and use a respirator, observing all safety precautions (Appendix 1 Safety in Handling Photographic Chemicals). 

Sepia Intensification Bleach and redevelop sepia toners, such as Ansco 221 Sepia Toner or Kodak T-7a Sulfide Sepia Toner, are more effective than chromium intensifier and will provide maximum archival protection for your negatives. The reason for the latter is explained more fully in Chapter 10,Toning Prints Protective Toners, though simply put, converting an image from silver metal to silver sulfide makes the image as permanent as it possibly can be. 

Uses Bleaching ingredient in tray cleaners and chromium intensifiers. 

Chromium in steel Discussion. The chromium in the steel is oxidised by perchloric acid to the dichromate ion, the colour of which is intensified by iron (III) perchlorate which is itself colourless. The coloured solution is compared with a blank in which the dichromate is reduced with ammonium iron(II) sulphate. The method is not subject to interference by iron or by moderate amounts of alloying elements usually present in steel. 

However the second question, whether the Cr+3 species either underwent some chemical change so that they became inert in the solution or Cr+3 ions were not available to DPC for complexation from the existing dichromate ions remain to be explained. Since either oxidation (c) or reduction (b) would occur in the solution in the given set of experimental condition, another experiment was performed to ascertain the cause of decomposition of Cr-DPC complex resulting into the decolourisation. A current of N2 gas was purged into the decolourised solution for about 10 min to remove all dissolved 02 gas from the solution and create an oxidation free atmosphere in and above the solution in the flask. The solution was sealed and left for an hour. The colourless solution changed to feebly pinkish colour and intensified over night (about 10 h). This confirmed the restoration of chromium ions to +3... 

The list of intensifier formulas includes uranium, silver, copper, selenium, chromium, mercuric chloride, and mercuric iodide. Some of the formulas, such as uranium, create a high degree of intensification but a low degree of stability. Others, such as chromium, do not intensify nearly as well, but the image is reputedly quite stable. 

Instructions for Chromium Intensification Two formulas for chromium intensification are given in the Formula section. Intensifier 1 gives more intensification than 2. 

Negatives to be intensified with chromium should first be hardened either in the fixer or after fixing in a hardening bath. Failure to do so may cause the gelatin to reticulate and ruin... 

Chromium in steel forms a carbide that hardens the metal. The chromium atoms may also occupy locations in the crystal lattice, which will have the effect of increasing hardness without affecting ductility. The addition of nickel intensifies the effects of chromium, producing a steel with increased hardness and ductility. 

In silicides, formed with the participation of atoms of silicon, which has a very low ionization potential, these peculiarities are intensified, and while practically all silicides having isolated silicon atoms possess metallic properties, the higher silicide phases of metals not having very high acceptor characteristics (iron, manganese, rhenium, chromium) are semiconductors. 

---