Bleaching prints

These rosin-based sizes, whether paste, Hquid, or emulsions, can be used to size all grades of paper that are produced at acid pH. The latter include bleached or unbleached kraft Hnerboard and bag paper, bleached printing and writing grades, and cylinder board. In addition, polyaluminum compounds have been used in place of alum, most notably, polyaluminum chloride (48), which can reduce barium deposits where these have been a problem. The barium chloride by-product is more water-soluble than barium sulfate. Other polyaluminum compounds such as polyhydroxylated forms of alum and polyaluminum siHcosulfate have been evaluated as alum replacements. 

There are three methods for bleaching prints overall, local, and spot. 

Fixer that has been partially exhausted will cause bleached prints to stain more easily. At the same time, ferricyanide bleach rapidly destroys fixer. Use fresh fixer and discard after the bleaching session after neutralizing it by dumping the remaining bleach solution into it. Plain Hypo is useful for this purpose as it uses only one ingredient and must be discarded after use anyway (Formulas Fixers Plain Hypo). 

Prints should be washed thoroughly and then bleached while wet (if they have previously been dried, rewet before bleaching). Bleach until the black image is converted to a very light brown color, about 1 minute. Wash the bleached prints for 10 to 15 minutes in running water. The bleach can be reused. 

Immerse the well-washed, bleached prints in the redeveloper. Redevelopment should be complete in about 1 minute, with constant agitation. After redevelopment the prints should be washed for about 30 minutes and then dried. If the toner leaves sediment immerse the print for a few seconds in a 3% solution of acetic acid, after which a 10-minute washing is necessary. 

Prints to be toned should be first soaked in cold water until limp, and then placed in Solution A until bleached. This should take about 60 seconds or less. The bleached prints should be immediately transferred to running water for at least 30 minutes. 

Bleached prints are placed in Solution B for 45 seconds to 1 minute until the deepest shadows are toned. Wash for 4 to 6 minutes excessive washing being undesirable because of... 

Dilute 1 10 with water. Tone the bleached prints for 3 to 5 minutes with continuous agitation. Rinse the prints for 5 minutes in Berg Bath (or HCA) and wash for 30 minutes. 

Dilute 1 9. Bleach prints before immersing in the selenium-sulfide stock solution. 

The bleached print is placed in one of the following toning baths and left until toning is complete. 

Rewash the bleached print until the water is perfectly clear. This may take as long as 1 hour in running water at about 70F/21C. This is the most critical step as any residual bichromate will stain the print during redevelopment. 

Wetting and scouring agent. Used in scouring, bleaching, print washing, and dyeing. 

Desizing Scouring Dyeing Final rinsing bleaching printing... 

Uses Detergent for textile dyeing, bleaching, printing and finishing operations ... 

Plastics can be used to make erasable printing media by a number of different techniques. Photo changing dyes could be incorporated into the structure of the plastics. The printer could change the dye to the colored form to read, and the material can be bleached with another unit that would reverse the photo coloring process. An ionic type plastic can be incorporated into the plastics and used to color the printed area by the use of an indicator type reaction with an organic acid or base. Another method would be to use a thermal printer in conjunction with liquid crystal type materials that would alter the state of the liquid crystals in the printed areas. Applying heat and electrical fields to the printed sheet would erase the printing. 

Bleached or unbleached kraft process wood pulp usually converted into paperboard, coarse papers, tissue papers, and fine papers such as business, writing and printing... 

Gedruckt auf saurefreiem, chlorfrei gebleichtem Papier-TCF / Printed on acid-free and chlorine-free bleached paper... 

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