Colour streaks

Similar to thermoplastics, pigments and dyes are sensitive to excessive processing temperature and residence times. If thermal damage is the reason for colour streaks, they should be considered as burnt streaks. 

Left Colour streaks due to an incompatible masterbatch Right Orientation of metal-effect pigments caused by the flow... 

The brush method here the substances to be separated give a colour test with a reagent. The developed column is extruded from the tube and streaked lengthwise with a brush dipped in the test reagent the colours... 

A writing test is also made by stretcliing a good sheet of paper in a kind of frame which keeps it taut. The sheet is placed at an angle of 450 to the horizontal and a given quantity of the ink allowed to flow 011 to it from a pipette with a very narrow orifice so as to form a streak three days later the streak is examined to sec if it is dry, what the colour is and how it resists the action of air, light and different reagents. 

In semi-automatic moulding the operator may inspect each unit for features including colour, dispersion and uniformity of colour, standard and uniformity of gloss or mattness, and the presence or otherwise of defects like silver streaks or stringing. However, it is preferable if assessments can be made in numerical terms, expressed in units that may be compared quantitatively and subjected easily to statistical treatment and analysis. It is often convenient in the course of... 

Fe203.H20, is a common ore which contains about 5 per cent, of water. It occurs as an earthy deposit frequently known as red haematite and as red ochre it is also found in a compact, fibrous condition, and in botryoidal and stalactitic forms, similar to limonite, for which ore it has frequently been mistaken. It may usually be distinguished by its redder colour, its red streak, and its greater hardness. Hardness 5 to 6 density 3-56 to 4 7. When heated in a tube it splinters in a characteristic manner, which serves to distinguish it from limonite and other ores of analogous composition. 

The crystals are usually blackish brown in colour, but appear red by transmitted light. They yield a red streak hardness 5 to 5 -5 density 4 0 to 4-4. 

The theoretical percentage of metallic iron is 48 3. Hardness 3 5 to 4 5 density 3 7 to 3 9. It is brown or grey in colour and leaves a white streak. It readily oxidises when wet, being converted into limonite. Siderite from East Pool Mine, Cornwall, has been found containing cobalt, nickel, and even indium and rubidium in small quantity.6... 

Iron pyrites, pyrite, marquisite, or mundic is the name given to a brass-coloured sulphide of iron to which the formula FeS2 is usually ascribed. It often occurs in coal, and is known by miners as brass or fool s gold. The spontaneous combustion of coal is frequently facilitated by the oxidation of iron pyrites to iron sulphate.6 It often crystallises in cubes, the faces showing striations but a very characteristic form is the pentagonal dodecahedron, usually termed the pyritohedron. Hardness 6 to 6-5 density 4 8 to 5-2. It leaves a greenish or brownish-black streak. 

Cobalt-nickel pyrites, (Fe, Co, Ni)Sa, has been found in Westphalia as small cubic crystals, steel-grey in colour, giving a greyish-black streak.3 Density 4 7, hardness 5 to 5 5. Iron nickel pyrites, (Fe,Ni)S2, occurs in Norway 4 and in the Sudbury district, Ontario.5... 

Lolingite, FeAs2, occurs in Saxony and Norway in rhombic crystals. Hardness 5 to 5 5 density 6-8 to 8 7. Greyish m colour, it gives a greyish black streak. When heated in an open tube a white sublimate of arsenious oxide or white arsenic S5 is obtained in the absence of air metallic arsenic is volatilised to a dark sublimate. 

It crystallises in tabular hexagonal scales belonging to the hexagonal system, and possesses a steel-like lustre. The edges are ruby-red in colour, and give a red streak. Density, 5-187 to 5-193.4... 

When worked, jet produces a brown dust, and when rubbed across a rough sur ce will leave a mid-brown streak of colour. 

Bois duxci is often mentioned as a simulant for jet but was in fact seldom used because it was formed in large, steel moulds, whidi were not suitable for the production of small items. It was a mixture of hardwood flour and ox blood, coloured with lampblack (a form of soot). It took a good, detailed imprint, was durable, and had its own niche, being used for plaques, barometer cases, inkwells aiul other large items (Fig. 13.2). The material gives a brown streak, but the words Bois Durd often appear moulded into the back or bottom of an object. 

Celluloid was one of the early plastics that was used in numerous ways. It was made of cellulose nitrate and was extremely combustible, but a safer version, cellulose acetate, was later developed. Dyed black, they are reasonable imitations of jet but th have a plasticy look and feel. Black celluloid gives a fldnt, black streak. Baikelite, or phenol formaldehyde, could be dyed any colour and was widely used. When dyed black, it was also a reasonable jet imitation, but it dulls with age and has a plasticl look and feel. Black Bakelite gives a black streak. 

Dyed coral may show streaks, patches, or accumulations of dye around any holes or cracks. The dye is oiJy on the surface, so an area that has been chipped or cracked after the material was dyed may show a lack of colour (Fig. 11.13). 

Material Weight Colour Lustre Fed Fracture lOx lens Work method Links/ fitangs Streak Burning aroma... 

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