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Commercial dishwashing and porcelain

Published by:
Arbeitsgemeinschaft Gewerbliches Geschirrspülen
[Commercial Dishwashing Association]

Feithstraße 86
58095 Hagen, Germany
Phone: 02331/ 377 544 – 0
Fax: 02331/ 377 544 – 4
e-mail: info(at)


What is porcelain?
Porcelain is a ceramic material. After treatment of the basic material ”Kaolin, Quartz and Feldspar”
follows a bisque firing at approximately 900 degrees, then the glaze, and glost-firing at temperatures
ranging from 1.350 to 1.450 degrees. Porcelain comes both, with and without decoration.

How can porcelain be recognized?
The mostly used porcelain has a pure white body, less common is porcelain with a coloured body.
Unlike earthenware (pottery) and stoneware, which both comes with a porously, non-translucent,
coloured body - porcelain is translucent when held against the light and produces a clear sound.

The features of porcelain
The hardness of porcelain guarantees a high level of chemical and mechanical resistance and
consequently a long usability. Neither chyles nor salt may infiltrate the surface.

Glazed porcelain has a highly impermeable, hygienic surface and a great heat storage capacity.
Porcelain is readily wettable

Do those features make automated dish washing easier?
Food residues can be easily removed of the smooth surface. Neither water nor food residues can
infiltrate the surface. That´s highly significant for hygienics.

Great heat storage capacity along with the rinse aid ensures efficient drying, aided by the great
wettability of porcelain.

Does cleaning undecorated porcelain in a dishwasher cause any difficulties?
There are no problems, as long as detergent and rinse aid are dosed correctly,
(cf. technical information sheet ”Commercial dishwashing & dosing”).

How about decorated porcelain?
Problems are rarely encountered any more even with decorated porcelain.
Porcelain surfaces featuring dark colour shades can also be cleaned and rinsed quite efficiently
in commercial dishwashers, provided that high water hardness is avoided and the salinity of the
water is not excessive.

However, there might be difficulties for darker colour shades if the salinity is too high, because the
high evaporation residue is conspicuous against the dark background (cf. technical information sheet
”Commercial dishwashing & water“).

Distinctions among décor:
We distinguish between underglaze-, inglaze- and onglaze decorations.

Underglaze decoration: protected by glaze, firing temperature at approx. 1.400° C.

In-glaze decoration: applied onto already glazed china. At firing temperatures ranging from
1.150° C to 1.250° C, the colours sink in the re-emollient glaze. During this process the
colour pigment becomes refounded by the glaze and therefore much better protected.
Porcelain with in-glaze and underglaze decorations is dishwasher resistant.

In-glaze decorations are referred to as either ”sink in”- or ”fast-fire” colours.

On-glaze decoration: firing temperature at approx. 830° C. Notwithstanding more stable colour
palettes and elaborated workmanship, the durability for the industrial sector is not to be
compared to in-glaze and underglaze decorations.

Hand-painted porcelain and precious metal decoration: Although that the adaption of those colours
to the requirements of automated dishwashing is more difficult, the adjustment for precious metal
decorations was achieved meanwhile.

If the manufacturer declares precious metal decorations as dishwasher-proof, there are
no objections to it.

What should be noted when purchasing porcelain that will be exposed to automated dishwashing systems?
Both practical and aesthetic reasons should be considered when selecting porcelain for commercial use. Particularly suitable are functional shapes, e.g. smooth, even, wide open and rounded forms, without troughs or double walls for better wettability. The mostly used tableware in hospitals, canteens and catering trades is porcelain featuring in- and underglaze decoration. Please use qualities, which are especially declared for the industrial sector by the manufacturer.

Can traditional bulbous shapes also be cleaned in a dishwasher?
In principle, yes. However, it should be considered that in dishwashers not only the surfaces have to
come into contact with the detergent solution, but primarily also have to be reached by a powerful
water jet. This is not always possible for dishes with pronounced bulges and/or spray shadows and the
cleaning result could turn out to be poor.

Are the dishes also being dried?
During the contact time with the hot detergent, the porcelain will be heated accordingly. Among addition of a rinse aid to the clear water, the surfaces are fully wetted. The residual water drains away film-like of the heated dishes. The remaining wetness dries by the porcelains body temperature or downstream drying.

Common porcelain dishes accumulate sufficient heat to ensure this procedure, provided that the correct rinse aid film accrues by exact dosage of the rinse aid. (cf. technical information sheet, ”commercial dishwashing & dosage”).

Are there any limits to the durability of porcelain?
Porcelain has a long service life. Mechanical influences such as stacking and scouring may cause
scratching and ablation of the glaze.

Porcelain dishes with damaged glaze surfaces are considerably more difficult to clean and the wash
results are far from being satisfactory. It is advisable to replace any damaged items.

What surface changes may occur?

If dishes frequently skim along metal surfaces, discolorations at the contact points may occur (metal abrasion). From there it may be carried over to the entire surface whilst stacking the dishes. Those discolorations can not be removed by dishwashing.

What must be considered for dishes featuring induction coating?
Those dishes are equipped with a metal coating at bottom side, which is heated by induction. The metal coating must be so designed, that there are no problems washing them together with uncoated porcelain. By frequent temperature fluctuation and chemical influences discoloration of the coating may occur, however, this is physiological credible.

Please use qualities, which are especially declared for the industrial sector by the manufacturer.

The member firms of VGG ensure expert advice 
This memorandum, carried out by skilled practitioners, should call the readers attention to the fact that industrial machine dishwashing cannot be carried out successfully without appropriate involvement of all parties, Only the understanding of technical processes and consequential coherences, the cooperation of those involved –particularly the operator of the dishwasher and its staff, as well as the regularly service of the dishwasher, dosing- and water-processing unit by the manufacturer, lead to excellent cleaning results.

Ongoing cooperation between the manufacturers of dishwashers, detergents and cleaning items ensure persistent, optimum alignment to the requirements in practice - to the benefit of common customers and our environment.

Any enquiries regarding this technical information sheet
”Commercial Dishwashing & Porcelain” please contact:

Arbeitsgemeinschaft Gewerbliches Geschirrspülen
[Commercial Dishwashing Association]
Feithstraße 86
58095 Hagen, Germany
Phone: 02331/ 377 544 – 0
Fax: 02331/ 377 544 – 4