Developing agents toning developers

Fig. 24. Representative cross-linking systems employed in negative tone CA resists, (a) Epoxy polymers requiring organic solvent development, (b) PHOST-based cross-linking systems requiring aqueous development, (c) Monomeric cross-linking agents used in PHOST matrix polymers.

Lesser amounts of sodium thiocyanate are used in color toning photographic paper, as a stabilizer in rapid film development, and as a sensitizing agent in color negative-film emulsions. It is also used as a brightener in copper electroplating. 

Method 1. The classic developing agent for creating cold tones on bromide papers is amidol. However, PQ developers using organic antifoggant, such as benzotriazole, will also increase the amount of cold image tone in a print (Formulas Paper Developers, Blue-Black Developer). In either case the results are usually very subtle. 

Notes Amidol is one of the finest developing agents for blue-black tones on soft-emulsion bromide paper. It is also capable of creating neutral-blacks with a fine scale and transparency in the shadows. 

Notes A derivative of hydroquinone, chlorhydroquinone was once a mainstay for warm-tone prints. Unfortunately, it is becoming increasingly hard to find, not because it is not useful as a warm-tone developing agent, but because it is both expensive and dangerous to manufacture. 

None of the paper developers in this section is written in stone. Many of them were created by photographers, not unlike you, who were experimenting with various proportions of developing agents and alkali. Feel free to alter any of the formulas. If your new brew gives you the tone/color, look, and feel you re after, great. If not, you may lose a few sheets of paper. 

Stebbins characterized the thresholds for detection of sound over the range of frequencies normally detectable in the monkey and the effect of an ototoxic agent on these thresholds. This was done by training the monkey to keep its hand in contact with a sensor until it detected the onset of a tone and to break its contact upon detection of the tone. Intensity of the tone was then varied for each frequency tested to determine the intensity at which the monkey was unable to detect the tone. Stebbins was thus able to follow the development of hearing loss produced by an ototoxic antibiotic, from initial high-frequency loss to later low-frequency loss. These changes in hearing in the monkey were correlated with the pattern of receptor loss in the inner ear. 

MAO inhibitors were at the center of interest. Both as experimental tools and as therapeutic agents MAO inhibitors had an important influence on the development of the widely accepted hypothesis that 1. depression is associated with diminished monoaminergic tone in the brain, and 2. depressed patients treated with antidepressants become elated because of enhanced biological activity of monoamine transmitters in the central nervous system. 

Figure 2 Thin layer chromatography plate (K6F - Whatman) traces of the standard extract labelled at 100,000 uic (top) and the MAP extract (bottom). The plate was eluted in a hexane propanol mixture (92 8) and did not require any developing agent given the deep coloration of the extracts. For the purpose of reproduction we have digitised the plate at 16,000,000 colours and converted the digital file into a 256-tone gray-scale one. Note that despite this dramatic graphical loss in resolution the differences between the two products are readily observed.

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