Vitreous Porcelain – a Ceramic From the Stoneware Family
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The explanation of the ceramic type of “Vitreous” requires the full name to be given: Vitreous China. As we explain in detail on our page “Chinaware”, the word “Chinaware” does not stand for “porcelain”, but rather for a ceramic collective term. On the traces of Vitreous we go to the United States of America and read there in a study of the “Vitreous China Plumbing Fixture Association” from 1941 detailed treatises about possible solutions for the hardening of sanitary ceramics. “… rising energy costs require a reduction of the firing temperature by a higher flux content and achieve sintering below 1,000 °C in the form of a densely fired body by means of crystalline and vitreous components. For this group of materials we propose the name ‘”Keramvitro”…”
This explains why the market leader for Vitreous China is the American sanitary ware brand “American Standard”. In the German terminology of porcelain production, the term “Vitro-Porzellan” was first defined in 1930 and is used in laboratories to compare with hard porcelain.
Traditionally, Vitreous China has a high proportion of light-firing clays (like earthenware) and a low proportion of kaolin (like porcelain), feldspar, quartz and pegmatite. Today’s manufacturers of Vireous porcelain advertise with the designation “Alumina vitrified clay body” which means “a clay body enriched with alumina”. Not a syllable about kaolin! Further we read in the German version of a brochure of the company Steelite “…are produced with a clay body enriched with alumina…”.
Vitreous China thus belongs to the stoneware family!
Similar to porcelain, Vireous can be produced in classic firing – i.e. biscuit and glost firing – or in mono firing. Again, the relationship between first firing and glaze firing is characteristic of the stoneware family.
- biscuit firing 1.240 – 1.300 °C
- glost firing 1.000 – 1.200 °C
This explains why all of the “Alumina Vitrified” tableware we commissioned for laboratory testing achieved a maximum Mohs hardness of 5. Genuine hard porcelain, however, has a hardness of 6 and thus achieves a 20% higher degree of hardness in terms of cut resistance and corrosion resistance.
Vitreous in the gastronomy
An English supplier of Alumina Vitrified is outstanding. Steelite is an internationally successful company. Many different materials, including melamine, are successfully sold under this brand. In terms of design and form our compliment and recognition. However, a lower cut resistance of flatware (plates and platters) and especially glaze corrosion can spoil the fun of tableware relatively quickly. Although the glaze of the vitro-cullet is harder and more scratch-resistant than that of ordinary stoneware, it cannot compete with hard porcelain.
Chemical detergents and commercial dishwashers are the ore enemies of Vitreous tableware. One may argue about whether the plate, thanks to its mechanical resistance, would have become so “old” that corrosion could occur at all, but the guest should no longer be presented with such a plate.
Vitreous ceramics – just like Durable and Arcopal tempered glass tableware – have a place in the catering industry! Wherever the mechanical stress is higher than the long-term use, break-resistant crockery can be used. Better hard ceramics or tempered glass than melamine, plastic or plastic, because that is not at all in keeping with the new spirit of the times! Vitreous China and Durable are the real rivals of hard porcelain.
About the plate above:
We manufacturers of tableware issue a declaration of conformity according to “LFGB” for our goods – but all of them only for undamaged tableware! If the porcelain is damaged – and this includes cut marks, cracks in the glaze and corrosion as above – suitability for food contact is no longer guaranteed. Externally damaged crockery is no longer suitable for food contact. The rule of thumb applies here: The lower the quality class of the tableware, the higher the risk for the consumer!
Vitreous at Holst Porzellan
We do not carry any “Vitreous” quality class tableware in our collection, and we see the much higher gastronomic value – and above all the long-term value – in the “Alumina Porcelain”, “High Alumina” and “Ultra Alumina” quality classes, and of course in the classic “Hard Porcelain” range. The three types of alumina porcelain belong to “real” hard porcelain due to their firing temperature and raw material composition and additionally offer the user mechanical stability like the Vitro or Durable tableware.
For a better differentiation of the ceramic types you can also read our article Quality classes of ceramics.