The most common is thin scratches in the glaze. Under the microscope you can see that they consist primarily of short (1-5 mm) parallel scratches. The foot of the plate above usually causes this by rubbing on the glaze surface of the lower plate. Scratches appear most often in the center of the surface of the plate, which is due to the fact that the plate is usually not placed centrally in the pile but is placed at an angle in the pile and pushed into place. It is the friction between the glaze and the foot and the weight resting on the foot, which are main factors that cause scratches. The more plates you place in the pile you are putting into the stack of plates already in the cupboard, the heavier they are and the risk of scratches increases. In order to minimize this friction/wear from a manufacturing perspective, Rörstrand polishes the bases of its plates using a 4-stage, wet polishing machine before they are sold to the customer.
The customer can also reduce wear by:
First: Always use rinse aid in the dishwasher. People with dishwashers will note how much rougher porcelain is when the rinse agent runs out.
Second: Do not handle wet plates as clean water increases the friction between porcelain surfaces.
A common misconception is that a glazed base will reduce the risk of scratches. This misconception comes from the fact that glazes with a high lead content mean less friction. Types of porcelain with glazes with a high lead content previously often had glazed foot (earthenware, bone china). It is unusual for glazes with a high lead content to be used nowadays.
Another misconception is that sharp knives cause scratches but even the sharpest of knives are not hard enough to cause this to happen. However, if you press really hard with a sharp, tempered knife you might be able to damage the glazed surface.
Black marks on the plate:
In most cases, black marks occur with cracks. The black is actually metal from stainless steel. The stainless steel is relatively soft and cannot be made harder and it makes dirty marks on the porcelain if pressed quite hard against the surface. Stainless steel is found in the kitchen in sinks, saucepans, whisks, ladles, etc. but primarily in cutlery. As it is mainly knives that are pressed hardest against the surface of plates, the majority of cutlery manufacturers now make serrated knives from some sort of tempered steel. (It is not worth making serrated knives from non-tempered stainless steel as the serrated edge would wear down quite quickly.)
Using only a fork to eat is the most common way of causing black metal marks as you then need to press relatively hard to cut through food. The glazes that blacken most quickly are matte glazes, but these are also the glazes from which it is most easy to remove the metal. Blackening occurs without pressing hard but does not stick as stubbornly.
Blackening can also be blamed to a certain extent on friction, and rinse aid in the dishwasher reduces friction. These porcelain properties are largely independent of manufacturer. One difference, which may occur between different manufacturers, is polishing of the base and gloss or matte glazes.
