Plane bottom

Plane bottom - a functional feature of hotel porcelain

Definition "Plane bottom"

In the porcelain industry, a flat bottom is a smooth, unglazed bottom. This shows the naked body of the respective porcelain article. Since real, highly fired hard porcelain is of high density and low porosity, a plane bottom does not affect the functionality of the porcelain in any way.

Function of the plane bottom

The production of porcelain articles with a plane bottom depends mainly on the intended use. Porcelain, which in the broadest sense is intended for conventional preparation, e.g. oven porcelain, or keeping food warm, usually always has a flat base. If the porcelain were to have an adjustment ring, as with a normal plate, the heat could not be transferred evenly to the porcelain body. Depending on the height of the collar, even large areas of the porcelain item could not come into contact with the heat source at all, so that much energy and efficiency would be lost and the bowl, bowl or plate would lose its functional properties.

The plane bottom ensures - as the name suggests - that the bottom of the porcelain article lies flat, i.e. smooth, on the heat source, thus ensuring optimum heat transfer from the source to the food placed on it.

In certain ranges we have therefore designed our porcelain with such a heat-conducting flat base, e.g.

• Gastronorm containers
• Gastronorm plates
• Almost the entire range of ovenware
• Many special articles for hospital & care
• Presentation bowl Bateau flag shape

Heat sources for porcelain with plane bottom

Porcelain with a plane bottom is made for contact heat, i.e. all types of heating and warming plates that emit thermal energy on their surface by radiation. Conversely, the contact also works in the cold area, i.e. to keep food cold and fresh in porcelain with a flat base on appropriate cooling elements.

Induction heat & plane bottom

We at Holst Porzellan cannot use induction heat - and by the way, we know of no other manufacturer who can realize the perfection underlying the material of porcelain with an inductive heat generation equally perfectly. Inductive tableware always requires a metal-containing coating (decoration), which is subsequently fired onto the porcelain. The very word coating describes its finite life. It is difficult to determine the metal content and distribution on the decorative paper, so there are surfaces that can convert more - and others the less - inductive radiation into heat. In plain language: On the left, the sauce burns, while the meat in the middle remains cold. And porcelain that does less than 1,000 rinses does not get into our homes.

Ceran hobs and plane bottoms

Ceramic hobs and ceramic hotplates are made of extremely heat-resistant borosilicate glass, as used in laboratories or on the space shuttle. Market leader Schott gives a value of 480 Knoop's hardness for the hardness of its borosilicate glass, which according to Mohs corresponds to about 2.5 to 3.5. The highly fired, unglazed porcelain shards have a hardness of 5 to 7 Mohs and thus "scratch" the refractory glass. In other words, the ceramic field cannot damage the porcelain. Conversely, the extremely hard porcelain destroys the soft glass when pushing and working on the hob. From the porcelain point of view, you can therefore use porcelain with a flat base on ceramic hobs without any problems - only the other way round.

Stainless steel work tables and plane bottoms

Here it behaves in the same way as shown above with the borosilicate glass. When porcelain is moved back and forth on stainless steel worktables, the flat base acts like an emery paper that rubs off tiny components of CNS 18/0 and also CNS 18/10. Although the porosity of the porcelain makes it impossible for these metal particles to penetrate, an unattractive, mostly grayish discoloration forms on the porcelain floor. This abrasion definitely has no influence on the usability of the porcelain article itself, it just looks unattractive.

Rechauds and plane bottoms

Rechauds usually work with candles, burners, fuel paste and similar, directly acting heat sources. This type of thermal irradiation is always punctual and not uniform, large-area. We have tried and tested for a long time whether a different heat emission from a plane bottom to a glazed surface can be detected. Really measurable for table and blackboard use, we could not find any differences. The only difference is that soot-containing fuels pollute the plane bottom much more than a glazed bottom. Therefore, there is no real benefit for the use with chafing dishes and warmer when using porcelain with a flat base.

Cost factor plane bottom

Oh, dear... ask a porcelain expert how much "something" costs... We at Holst claim that the production of a bowl with a flat bottom is basically more expensive than the production of an equivalent bowl with a ring and glazed bottom. However, as you can read in the following point, the "flat bottom" design can lead to far less waste in the end, which in turn justifies the additional effort for removing glaze residues and polishing. Since, as already mentioned, porcelain has a Mohs hardness between 5 and 7, the corresponding grinding stones and grinding papers must be of extremely high quality. Such "diamond paper" costs a lot of money and wears out a lot after only a short period of use. 

Therefore, the smoothness and flatness of porcelain with a plane bottom is always directly related to the price. Here the rule of thumb applies: The larger or the cheaper a porcelain item is, the coarser its flat bottom is. Small uneven spots, bulges or holes do not impair the function of the flat bottom. The porcelain should simply not "dance" - i.e. lose its stability - or show sharp-edged residues.

Production-related execution of plane bottoms

For the sake of completeness, it should be mentioned that porcelain with a plane bottom is subject to lower shrinkage tolerances than equivalent porcelain with an adjusting ring and glazed bottom, depending on the size and design. This is especially true for calipered porcelain used for food distribution. In the case of functional tableware that has to be dimensioned exactly, such as system trays for compact systems, the "flat base" design is probably more a matter of calibration, i.e. accuracy, than the user benefit of better thermal conductivity.

Contamination of porcelain with plane bottom

It should be clear to every user that porcelain with a plane bottom will attract foreign matter over time, giving the appearance of dirt or a lack of hygiene. If this does not bother you, you can restore the porcelain bottom to a perfect condition with an appropriate cleaner - e.g. Etolit porcelain cleaner. This change, however, is a process that is neither unhygienic in itself nor does it ever come into contact with food or foodstuffs. It is the underside of a piece of tableware that usually neither guest nor patient should ever see - just like the cooker on the stool in the kitchen.