Colour depth

Gravure printing employs an intaglio process whereby the print area lies below the surface of the plate in small cells. The tone or colour depth may rely on the depth of etch (i.e. amount of ink which lies in the cells) and/or the number of cells per linear inch. All gravure is basically half tone (solid line gravure plates are used in some tampon or cliche processes). 

The relative colour depths of caustic soda-scoured and environmentally friendly bioprepared fabrics do not show signihcant differences. ... 

The beginnings of the enormous field of solid-state physics were concisely set out in a fascinating series of recollections by some of the pioneers at a Royal Society Symposium (Mott 1980), with the participation of a number of professional historians of science, and in much greater detail in a large, impressive book by a number of historians (Hoddeson et al. 1992), dealing in depth with such histories as the roots of solid-state physics in the years before quantum mechanics, the quantum theory of metals and band theory, point defects and colour centres, magnetism, mechanical behaviour of solids, semiconductor physics and critical statistical theory. 

It is advisable, wherever possible, to make a preliminary determination of the concentration of the unknown solution by adding from a burette a solution of the component in known concentration to a Nessler tube containing the reagents diluted with a suitable amount of water until the depth of colour obtained is practically the same as that of an equal volume of the unknown solution also contained in a Nessler cylinder and standing at its side. A series of standards on either side of this concentration is then prepared. 

Figure 10.8 p(4 x 1)S Ni(l 10) surface, (a) High-resolution STM image, (b, c) Top and perspective views, respectively, of model structure. The sulfur atoms are black and the copper atoms are grey with increasing depth indicated by darker colours. (Reproduced from Ref. 30). 

Pearlescent pigments give rise to a white pearl effect often accompanied by a coloured iridescence. The most important pearlescent pigments consist of thin platelets of mica coated with titanium dioxide which partly reflect and partly transmit incident light. Simultaneous reflection from many layers of oriented platelets creates the sense of depth which is characteristic of pearlescent lustre and, where the particles are of an appropriate thickness, colours are produced by interference phenomena. Pearlescent pigments are used in automotive finishes, plastics and cosmetics. 

Several books describe the background to this topic. Perhaps the best general introductions come from the Royal Society of Chemistry Colour Chemistry by R. M. Christie, RSC, Cambridge, 2001, is written for the beginner, but does extend to some depth. It... 

A slightly more in-depth study of colour is afforded by The Physics and Chemistry of Colour by Kurt Nassau, Wiley, Chichester, 2001. The author describes many everyday examples of colour, from peacock tails through to the Northern Lights, Aurora Borealis. Its Chapter 1 is an overview, and is probably a little highbrow at times, but overall is a fascinating read. 

Vat dyes are used to colour both components in pale depths on polyester/cellulosic fibre blends [44] but coloration of the polyester component in this case is more closely analogous to disperse dyeing (section 1.6.5). Anthraquinone disperse dyes resemble those vat dyes that are substituted anthraquinone derivatives and in both instances it is exclusively the virtually water-insoluble keto form that is absorbed by the polyester fibre. 

Quite small variations in disperse dye structure can markedly modify substantivity for polyester [89]. This is evident from Figure 3.4, where the two blue dye structures differ only in the 3-acylamino substituent of the diethylaniline coupling component. Replacing acetylamino by propionylamino in dye 3.74 increases the colour yield by at least 30% for a 1.5% depth applied to polyester fibre for 45 minutes at 130 °C. An even more striking example is provided in Figure 3.5, illustrating two isomeric greenish blue dyes applied to... 

Ammonium Salt of Eosin.-—Place a very stout filter paper on a flat-bottomed crystallising basin which is one-third full of concentrated aqueous ammonia solution, spread eosin to a depth of about 0-5 cm. on the paper, and cover the whole with a funnel. Very soon the light red crystals acquire a darker colour, and after about three hours they are completely converted into the ammonium salt, which forms dark red crystals having a green iridescence. When a sample of the material dissolves wholly in water the reaction is known to be complete. 

When the colourless carbinol base is treated with acid the quinonoid structure is re-formed and the dye produced. But on dissolving cautiously, with cooling, it can he seen that the colour attains its maximum depth only gradually. Hence the exceedingly unstable colourless carbinol salt is first formed it changes into the dye with spontaneous elimination of water ... 

By matching the intensity and depth of colour with standard stains, the proportion of arsenic in the substance may be estimated. Thus, a stain equivalent to the 1 ml standard stain obtained by performing on 10 g of a substance implies that the proportion of As is 1 part per million. 

The colour intensity of a solution is related to the concentration of the ions and the depth of the solution. By adjusting the depth of a solution with unknown concentration until it has the same intensity as a solution with known concentration, you can determine the concentration of the unknown solution. For example, if the concentration of a solution is lower than the standard, the depth of the solution has to he greater in order to have the same colour intensity. Thus, the ratio of the concentrations of two solutions with the same colour intensity is inversely proportional to the ratio of their depths. 

When the colour intensity is the same in both vials, measure and record the depth of solution in each vial as carefully as possible. 

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