Vitreous china
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| Vitreous china | |
|---|---|
| Material type | enamel |
| Physical properties | |
| Density (ρ) | 1.83-2.48 g/cm3 |
| Water absorption—over 24 hours | <0.5% |
| Mechanical properties | |
| Compressive strength (σc) | 400-800 kgf/cm2 (39226.6-78453.2 kPa) |
| Poisson's ratio (ν) | 0.5 |
Vitreous china is an enamel coating applied to ceramics, particularly porcelain, after they have been fired, though the name can also refer to the finished piece as a whole. This coating enhances the tougherness, density, and shine of porcelain, and it is a common choice for items such as toilets and sink basins.[1][2][3]
The development of vitreous china's closely follows that of other vitreous materials like glass, owing to the similar production process in terms of the materials needed and preparing and firing such. Because enamel is essentially glass applied to a substrate or surface to cover it, its production differs from that of glass by only a few steps.
The earliest known objects to be covered with a glaze are glazed stones made for jewellery, having been manufactured in Egypt as early as 4000 BC, in Mesopotamia from 5500 to 4000 BC, in Europe from 1400 BC, and in the Indus Valley from 4500 to 3500 BC.[4] The first instance of applying an enamel to a substrate occurred around 3500 BP in Mycenae and Cyprus.[5] The champlevé technique, which involves first placing a glass enamel powder on a substrate and then firing it, was the predecessor technique for applying vitreous china and was used by the Celts from the 1st century BC.[5]
Uses
Vitreous china is used in a variety of household and sanitaryware items such as basins, toilets, bidets, urinals, and bathtubs.[6][better source needed] Items that use vitreous china are usually ones that are best when kept clean and sanitary, with which a coating of vitreous china enamel helps. These same vitreous china items also benefit from having stains and spots removed easily due to the nature of their use.
Vitreous china can be occasionally found applied to kitchen countertops and related fixtures.[7] The low occurrence is due to vitreous china's fragility when exposed to blunt force from crockery and other kitchen items. Instead, materials like plastic and steel are more commonly used in kitchen fixture.
Vitreous china can also serve aesthetic purposes. Items applied with a vitreous china enamel for this purpose include plates and other chinaware in china painting, and Fabergé eggs.
Structure
Vitreous china, like other enamels, is a glass-particulate composite, that consists of glass (50-70 wt%) with non-silicate particles strewn about it that give it different properties.[8] Included in the vitreous enamel mixture is clay, which helps hold it all together and gives the necessary flexibility to form it into shape during firing, quartz which reduces shrinkage, and feldspar, which increases the liquidity of the mixture when fired into its vitreous phase, ensuring low porosity in the final product.[9][10]
After vitrification, vitreous china contains mullite, a crystal which forms as a result of reactions taking place in clay.[11] Not all quartz and feldspar liquify during firing, so some remain as "relict" (its pre-firing powder form) in the final vitrified product.[11]