Journal

‹ Back

The work of tile-making I - clay and tile forming

 

 

 

We know that the priory church at Lossenham, in common with many other religious buildings of the period, had decorated floor tiles over at least some of the floor area though, sadly, this knowledge is based on a modest number of tile fragments rather than any surviving areas of original floor. The tile floor was almost certainly, like other building materials, taken up and sold or otherwise repurposed when the priory fell into disuse after the reformation. Nonetheless, the fragments found in the archaeological investigations provide a starting point for exploring how these types of tiles might have been made, and whether this work could have been done with local materials. There is no evidence of pottery or tile-making having been carried out on the priory site, but it was not uncommon for this to occur with large building projects particularly, as here, where the raw materials were readily to hand. More generally, however, since there are no documentary records of how medieval tiles were made, the project provides an opportunity to do some practical experimentation which might contribute to the understanding derived from examination of medieval tiles themselves.

 

Most writing about medieval two-colour tiles provides some account of how they were made, though with widely varying levels of detail, derived from examination of medieval tile remains ^{1 2}. However, useful as these accounts are, when it comes to the nitty-gritty of actually making a tile they are, necessarily, sometimes speculative and leave many detailed questions unanswered. Experimentation may be helpful in evaluating some of the speculation, and answering some of the questions ³. To this end we have sought to reproduce some of the two-colour Lossenham tile designs, using materials on the site, and observing some of the practical considerations which must have applied to medieval tile makers.

 

A fragment of decorated tile from the Lossenham priory dig

 

The first challenge for the tile maker was finding a suitable clay — ideally close to hand. The number of tiles that it would have taken take to fill a medieval tile kiln depends, obviously, on the size of the kiln, but at an estimate of 5000 tiles ⁴, with a typical floor tile taking about 0.5kg of (wet) clay, this would represent over 2.5 tonnes of clay which had to be dug, transported and worked for each firing. Ideally, too, given the amount of clay required a tiler would want clay that could be used without needing much, if any, processing to remove things such as larger stones and plant roots. The medieval tiles we are working with, and others we have examined, typically have quite a lot of smaller stones and grit in the fabric, indicating the clay was used without the sort of preparation which might have been necessary if the clay were to be used for throwing pots.

 

Section through a Lossenham tile

 

The practice advocated by the tilers’ guild in 1468, of digging clay in the autumn then weathering it over winter before using it in the spring would have helped even up the consistency and moisture levels of the clay, and perhaps exposed some of the larger stones or other material, which could then be picked out by hand. It seems likely that no further preparation was carried out, aside perhaps for some kneading of the clay immediately before use. The inclusion of smaller stones and grit, whilst creating some potential complications at the decorating stage (as will be discussed elsewhere) may even have been advantageous in creating a tile body that dried more evenly and with less tendency to warp (reasons grog or sand are sometimes added to clays today ⁵). Keeping clay preparation to a minimum would save a considerable amount of work, though almost certainly result in an occasional ruined tile where a stone, hidden in the tile body, fractured during the firing.

 

Tile damaged during firing by fracture of a stone in the fabric

 

So far we have experimented with several of the different clays from Lossenham farm, in particular sites 4, 8, 9, 10 and 12 (see map and images). Two of these (sites 4 and 9) are looking the most promising for making tiles with unprocessed clay. The others either have too many stones and other debris in (which compromises later processes such as cutting and finishing the slip decoration), or have a shrinkage rate which does not match that of the white slip used for the pattern.

 

A mismatch in the shrinkage of slip and tile body clays during drying

 

 

One of the clays (site 10) which looked promising in terms of having few inclusions turned out to bloat severely, usually to the point of destruction, when fired. Interestingly, this is a clay we have previously used successfully but on that occasion the clay was taken from a spoil heap which had been sitting exposed to the weather for many months: perhaps part of the reason tile makers weathered clay over the winter. I am now doing the same with this clay and we’ll see if using it in the spring yields more success. Interestingly, both the most promising clays are associated with pockets of the same white clay as we are using for the decorating, which may account for their more compatible rates of shrinkage.

 

Having weathered the clay, kneaded it a little to mix it, the clay needs to be formed into a tile — usually square, and typically for the Lossenham tiles, about 120-140mm across and about 20mm thick. Most tiles today are made either by pressing clay into a plaster mould, cutting them out of a rolled-out slab of clay, cutting sections through an extruded block of clay, or, on a more industrial scale, by using a mechanical press to compress damp clay powder into a solid tile. However, there is general agreement in the literature that in medieval times forming tiles was almost certainly done in a mould, or form ⁶ — a wooden frame into which plastic clay could be pressed. What is less clear is exactly what form this mould took, since there are no surviving examples. We have experimented with various different designs:

 

Simple fixed frame mould, here screwed together and straight-sided, but can also be bevelled, and may have been fixed together using iron corner bands.

 

Lap-jointed mould - straight-sided but can be dismantled to remove the tile.

 

Lap jointed mould, with cut-aways on the joint and removable wedges,

allowing the sides to be removed more cleanly

 

 

 

Four-piece bevelled mould, held in place by blocks on a wooden board

 

All these work, in terms of pressing clay into them to form tiles, but the differences relate to the ease of removing the freshly made tile without distortion or damage, and whether the tile was made with vertical or bevelled sides. Where the final tiles were intended to have vertical sides, then clearly a vertical-sided mould would be used, but many tiles were made with bevelled sides (sloping inwards from top to bottom). Most accounts suggest these bevels were knife-cut ⁷ later in the process but, equally, it might have made sense to create the bevel when the tile was formed, reducing later work.

 

Based on experiments so far, in terms of speed of use and tile consistency, I would choose the moulds (particularly 2 and 3 above) that can be dismantled to release the tile, rather than a fixed frame where the tile has to be pushed out. But none of the accounts in the literature seem to consider multipart moulds as a possibility.

 

The release of the tile from the mould raises another question, which is over the use of some sort of releasing agent to stop the clay sticking to the mould sides or the board. Evidence from the presence of sand grains on the backs of many medieval tiles indicates a scattering of sand being used to stop the clay sticking to the backing board or bench ⁸, but the use of wood ash is another possibility ⁹: it would have been readily available, at no cost, and would also might have been more effective for dusting the sides of the mould. Both do work, and probably both would have been used, by preference or availability, but although I expected ash to be a good solution for stopping the clay sticking to the mould sides, my experience so far has not really confirmed that. The problem of clay sticking to the mould also makes using a fixed frame bevelled mould unsatisfactory as the tile has to be pushed out from the back, and the adhesion to the sides of the mould inevitably distorts the tile.

 

Distorted tile when pushed from a bevelled mould

 

One relevant issue may be that some of the natural clays tend to be rather more sticky than many manufactured clay bodies — presumably a result of more small particles in the clay. So with some of our clays, their tendency to stick to the mould is one reason why the multiple-part moulds are more successful.

 

A related point is that with clays that tend to be sticky it is advantageous to work with clay that is drier and less plastic than would be used in pottery. The challenge for working with stiffer clay is that it is hard to take a large lump of clay and press it into a mould, spreading it into all the corners. An alternative we have experimented with is to tear smaller pieces of clay off a lump and press these into the mould one by one. With a smaller piece of clay, even when stiff it can be pushed into the corners of the mould. Once the clay is proud of the mould a wooden mallet can be used to consolidate the clay. Such an approach appears to risk trapping air pockets in the clay, but while this is problematic in clay used for throwing, in tiles of this sort it is not really a problem. I have found no difference in failure rates between tiles made of single, or multiple pieces of clay.

 

Using smaller pieces of clay to fill the mould

 

 

Consolidating the clay

 

This approach has a secondary benefit which is that even when working with a lump of clay that has received very little kneading or other preparation, the process of building up the tile from many smaller pieces of clay is that it mixes the clay from throughout the lump. Interestingly, when you look at the sides and backs of medieval tiles, or at the internal structure where a tile is broken, there often seems to be evidence of the folds, layering, and little gaps which are typically a result of this process ¹⁰. From a production point of view, the time to fill a tile mould is quite similar using either method, but the piecemeal approach reduces the clay preparation time required.

 

Having consolidated the clay, cutting off the excess with a wire is straightforward. Did medieval potters have wire for cutting clay? We don’t know, but it would be possible to achieve much the same with a metal, or even wooden, blade. The top of the tile can then be levelled and smoothed with a wooden edge. Sometimes bits of grit or stones can be torn out of the surface during this process, and such holes need to be patched with some of the scraped off clay. It is often suggested that adding water to the top of the tile to facilitate this smoothing process is necessary, but I have found that while this works, it is not really required and over a long sequence of tile making, the mould and working area become progressively wetter, which is unhelpful. With decorated tiles, in particular, the surface will be further finished in the decorating process, so achieving a fine surface at this stage is not strictly necessary.

 

Finished tile surface, in the mould

 

Once the tile surface is finished then, it is possible that the tile would have been stamped with the impression of the pattern while still in the mould — and this will be discussed further in the second part of this topic - but, whether stamped or not, the tile would probably have had to be removed from the mould straight away to allow the next tile to be made (unlike a plaster mould where the tile needs to be left for a little while while the moisture is absorbed by the plaster). With a straight-sided, fixed-frame mould, a wooden block cut to exactly the size of the mould is needed to support the tile while it is pushed out of the frame and transferred to a wooden board. With the multi-part mould, the entire mould can be picked up and dissembled on the wooden board, then the mould parts reassembled.

 

Whichever process was used, speed would have been essential in producing the 4-5000 tiles needed for the next firing. My current average is about two and a half minutes to make a tile, though whether I could keep that up all day remains to be established!

 

Decorating, trimming, drying, glazing and firing remain to be done. But this journal entry is quite long enough, so these will be discussed in part II. In the meantime, we’ll let the tiles start to dry!

 

Drying tiles on rack

 

Notes

 

1. e.g. Eames, E., 1992. English tilers. British Museum Press, London; Eames, E., 1980. Medieval lead-glazed earthenware tiles in the Department of Medieval and later Antiquities, British Museum; British Museum Publications, London; Eames, E., 1985 English medieval tiles. British Museum Publications, London; Green, M., 2003. Medieval Penn floor tiles. Miles Green; Lewis, J.M., 1999. The medieval tiles of Wales. National Museums and Galleries of Wales; Stopford, J., 2005. Medieval floor tiles of northern England. Oxbow Books, Oxford; Van Lemmen, H., 2000. Medieval tiles. Shire Publications; Wight, J.A., 1975. Mediaeval floor tiles: their design and distribution in Britain. John Baker, London.

2. The purpose of this journal piece is not to provide a full review of this work, though I hope to discuss some of the ideas further elsewhere.

3. There is limited experimental work in this area, though examples can be found in: Haberly, L., 1937. Mediaeval English pavingtiles. Blackwell, Oxford; Drury, P.J., Pratt, G.D., 1975. A late 13th and early 14th century tile factory at Danbury, Essex. Medieval Archaeology 19, 92–164; Barbier, M., 1999. La conception des carreaux du moyen âge et de la Renaissance, in: Mayer, J. (Ed.), Pavement: Carreaux de Sol En Champagne Au Moyen Âge et à La Renaissance. Centre de Recherches sur les Monuments Historique, Paris. In addition, there is important work by the few current makers of medieval type decorated tiles (a listing of whom can be found at: heritagecrafts.org.uk/craft/encaustic-tile-making/)

4. Estimate from Green (Green, M. 2003. Medieval Penn floor tiles. Miles Green.); Drury and Pratt estimate around 11,000 tiles for the Danbury tile kiln (Drury, P.J., Pratt, G.D., 1975. op. cit.)

5. https://digitalfire.com/material/828

6. Eames, E., 1980. op. cit. However, in passing it is worth noting that the experimental archaeology project at Guedelon Castle, in France (https://www.guedelon.fr/en/) uses iron forms for making floor tiles (Secrets of the Castle (2014) BBC. Episode 3).

7. Eames, E., 1980. op. cit.

8. Eames, E., 1980. op. cit. p18

9. Company of Artisans, 2025. https://www.youtube.com/watch?v=kW8mW0aRCsM; Barbier, M., 1999. op. cit..

10. See images in the Journal entry ‘Conversation with a medieval floor tile’