How to fire the otherwise red-burning clay in a way to achieve a whitish colour? Testing burning technology on early modern pottery

Véninger Péter

Hadak útján. A népvándorláskor fiatal kutatóinak XXIV. konferenciája. Esztergom, 2014. november 4–6. Conference of young scholars on the Migration Period. November 4–6, 2014, Esztergom

MŐT Kiadványok 3.2 (2017) 785–801

DOI 10.55722/Arpad.Kiad.2017.3.2_34

Egy ma már ismeretlen kerámiaégetési módszer technológiáját próbáltam rekonstruálni. Valaha a fazekasok egy része képes volt arra, hogy fehér kerámiát készítsen olyan agyagból, amelynek magas vas-oxid tartalma van. A módszer lényege, hogy az égetés során kétféle színt hoznak létre úgy, hogy ezek keveréke együtt a lehető legvilágosabb legyen. A cikk folytatásában a fehérre égetett, engóbbal, mázzal díszített kerámiák készítéséről lesz majd szó.

Kulcsszavak: kísérleti régészet, kerámiatechnológia, égetés, fehér kerámia

The firing of pottery from true white-burning clays is a well-known method, and potters still use white-burning clays today. The ordinary (red-burning) clay can be burnt to a red colour due to the iron oxide it contains. It might seem an unusual idea that this ordinary clay can be burnt to a fairly light, almost white colour. However, among the archaeological finds, there are pieces whose white colour is not due to extra ingredients but to a special firing technique.

Potters today do not know and do not use this white-burning technique. The question then arises, how it is possible to make research into a technique that nobody knows today?

The commonly used testing methods of pottery are not suitable for testing the firing technique, so I had to find a method whereby it is possible to gain information about the firing process. To do this, I took advantage of two properties of ceramics; first, that colours created in the firing process can be changed during another firing, and second, that ceramics once burnt to a yellow colour cannot be reburnt to red. These two features can be used to show whether yellow burning had any role in the firing process of whitish pottery.

During the test, I reburnt light-coloured ceramic fragments and examined the change of colours. I identified two types of burning methods in this manner: one group had been first burnt to red and subsequently to gray, while the other group first to yellow and then to gray. In both cases, the mix of two colours has a whitish effect. With the refiring method, I managed to gather enough information so as to initiate further experiments in a wood-fired kiln. Because of the special firing technique, slip and glaze, in principle, could not be on the pottery; yet we find both slip and glaze on several white-burnt ceramic pieces. I intend to examine this problem in a next article.