Enamel colours

Cadmium Selenide. This compound, or the polyselenide, is responsible for the colour in selenium ruby glass. With some CdS in solid solution it forms the basis of Cd-Se red ceramic (especially vitreous enamel) colours the firing temperature must not exceed about 850°C. The presence of up to 3% V2O5 is claimed to stabilize the colour, blackening in the presence of a glaze or flux containing Pb is caused by the formation of PbSe. Cadmium Silicate. CdSi03, sp. gr. 4.9 m.p. 1240°C. 

Enamel. See enamel colour glass enamel vitreous enamel. Enamel-back Tubing. Glass tubing, the back half of which (the tube being held vertically) is seen to consist of white or coloured ply glass (q.v.)... 

Enamel Colour. A ceramic colour for the on-glaze decoration of pottery. Enamel Firing. In the British pottery industry this term is synonymous with DECORATING FIRING (q.V.)... 

Lead Antimonate (Naples Yellow). This compound, generally used in conjunction with tin oxide or zinc oxide, gives a good onglaze yellow for pottery decoration it is also used, with a lead borosilicate flux, as a vitreous enamel colour. 

Squeegee Process. See screen PRINTING. The term squeegee qil is used, particularly in the US industry, for the mixture of oils used to suspend a ceramic or enamel colour for silk-screen printing. Similarly, the term squeegee paste is used for the mixture of oils, colours and flux used in this process of decoration. 

A fault sometimes encountered with enamel colours on pottery-ware, the colour becoming detached from the ware during firing a common cause is lack of control during hardening-on (q.v.). 

Hunt, B. (1976) The true story of purple of Cassius, the birth of gold-based glass and enamel colours. Gold Bull, 9,134 139. Zsigmondy, RA. (1926) Properties of colloids. Nobel Lecture. Available at http //www.nobelprize.org,/nobeljprizes/ chemistry/laureates/1925/zsigmondy-lecture.html (March 31, 2014). Hervas-oliver, J.L. and Albors, J. (2012)... 

A vitreous enamel coating is, as the name implies, a coating of a glassy substance which has been fused onto the basis metal to give a tightly adherent hard finish resistant to many abrasive and corrosive materials. The purpose of modern vitreous enamels is twofold, i.e. to confer corrosion protection to the metal substrate and at the same time to provide permanent colour, gloss and other aesthetic values. 

Frit may be milled dry or wet. The long established dry process is used for cast iron baths and for chemical plant. Vitreous enamel application by a dry electrostatic method is being used on an increasing scale. In these cases, the frit is milled alone, or with inorganic colouring or refractory additives. This is achieved in cylinders using balls of porcelain, steatite or more dense alumina, or with pebbles of flint, to produce a fine powder of predetermined size. 

Decarburised steel is a mild steel that has undergone a heat treatment in a controlled atmosphere to reduce the carbon content to about 0-005 This type of steel can be used for white or coloured enamel direct to steel. 

In enamels for chemical plant such as autoclaves it is not only the degree of acid resistance which is important but also the freedom of the finish from minute flaws detectable by high frequency spark testing or chemical methods. The chemical methods depend upon a colour change when the reagent such as ammonium thiocyanate reacts with the iron exposed at the bottom of the pinhole or flaw in the finish. Alternatively, an electric cell can be formed via the exposed iron in the flaw and detected chemically. 

Glass polyalkenoate cement has a unique combination of properties. It adheres to tooth material and base metals. It releases fluoride over a long period and is a cariostat. In addition it is translucent and so can be colour-matched to enamel. New clinical techniques have been devised to exploit the unique characteristics of the material. 

A restorative material can be used for the aesthetic restoration of the front (anterior) teeth only if it is as translucent as tooth enamel. This is because colour matching depends on translucency as well as hue and chroma. 

Dental silicate cement is used for the aesthetic restoration of anterior (front) teeth because it is translucent and so can be made to colour-match tooth enamel. It is prepared by introducing powder into the liquid gradually in order to dissipate heat, although the exotherm is not so great... 

The most important use of selenium is as a pigment which gives a red colour to glasses and enamels. However, selenium is a catalyst in many chemical reactions and is widely used in various industrial and laboratory syntheses. 

The major use (60%) for coloured inorganic pigments, such as iron oxides, is in the construction materials industry. Here they are used to colour roof and flooring tiles, fibrous cement and mortar. Many inorganic pigments are used in coloured baking enamels for metal appliances. Chromium oxide is used in the refractory industry, not for its colour but because of its ability to improve the properties of bricks used in furnace linings. 

Fig. 2. Teeth demonstrating fluorosis. A high level of dietary fluoride has resulted in much of the enamel becoming opaque in patches, giving a mottled appearance. (Reprinted with permission from [48]. Copyright 2002 Mosby International Limited.) (See Colour Plate Section at the end of this book.)...

Ware and Glass Makers, to give a blue Colour to both Sorts of Ware, Tis also with Safre that they colour calcin d Pewter, in order to make the false Stone, which I ve noted in the Chapter of Enamels And lastly, with Safre it is that the azure Colour of Glass is produc d, as is before observ d, and of which is made the counterfeit Sapphires (117). 

The migration of water in teeth was tried to be visualized using fuchsine dye as a colorant ([103], rosaniline hydrochloride C19H17N3 HCI). Fresh human molars were immersed into a slightly acidic aqueous fuchsine solution. As was expected, the water penetrated fast via the nerve canal into the pulpa and especially the roots were dyed red from fuchsine migrating inwards as well from the sample surface as from the nerve canal. After several days, it could be observed that water had migrated into the gap between the enamel and the dentine (edj). Generally the intensity of the colour increased with time, and the dentine took up the colour more readily than the enamel. 

Oligophenylethoxysiloxanes are used as modifiers for various polymers to improve their weather resistance and other technical characteristics, as well as to increase the heat resistance of coatings. E.g., PES-50 is used to modify polyethers, aciylic and epoxy polymers PES-80 is used to modify alkyd and urea-formaldehyde resins. Besides, PES-80 is used as an additive in paints and enamels (to improve their flow properties, gloss and colour), as well as in concrete mixes (to improve the water resistance and durability of concrete works). 

Teeth have a transparent outer layer of enamel which is about 2 mm thick, and an inner layer of white dentine which surrounds the innermost pulp cavity where the nerves are located. Both the enamel and the dentine are calcium phosphate, a mineral that can exist in various forms, that of the enamel layer being hydroxyapatite, which is one of the hardest naturally occurring minerals. When this is exposed to fluoride it forms an even harder mineral fluoroapatite. Unfortunately both this and hydroxyapatite are slightly porous and this is why teeth become stained by chemicals such as polyphenols and other dark coloured substances that are present in coffee, tea, red wine, bilberries, blueberries, and cigarette smoke. (Staining can also be caused by tetracycline antibiotics, especially when taken by children whose teeth are developing. This type of discoloration is permanent, which is why such antibiotics are now only prescribed for adults.)... 

Enamelling consists of forming an adherent glass on the metal surface. Surfaces treated in this way are resistant to attack from acids and weak alkalis. The glasses may be coloured and formed into decorative patterns for household ware and jewellery and are prodcued from a mixture of oxides of silicon, boron, sodium, calcium, and lead. Secondary elements are also added, e.g. nitrates and manganese dioxide, which oxidise impurities, other oxides to aid adhesion to the metal surface, and pigments to impart colour and opacity. 

Dentine, enamel and cementum all have the same, or nearly the same, colour - typically an opaque cream - and they have the same lustre and can take the same, high polish. If there is any enamel on a piece of raw ivory it is usually removed before working. 

As herbivores, elephants other teeth are all molars. There are two teeth in wear on either side of the mouth, in both top and bottom jaws, and lihe the tusks, they also grow throughout the animal s life. They are worn away with chewii and are replaced by new teeth growing from the back of the mouth. This process is continuous so, if the elephant lives long enoi, the full complement of six sets of teeth will have been worn away, and finally the animal will die of starvation. The molars are seldom used for ivory as they are not homogeneous. They are made up of folds of dentine and enamel and are stripy cream and white in colour (Fig. 3.13). 

Suid tusks are hollow for much of their length. They are also slender and all of them curve to some degree (Fig. 3.6). In cross-section they can he squared or triangular and show irregularly aced concentric lines of dentine. Much of the exposed tusk may be covered with enamel and have furrows along its length. The creamy colour is not always even. 

---