The dimensions are nominal and are the manufacturers intended size of the finished item, few are precisely as stated. Variations are usually within a narrow range, most are within 1/16 inch (1.6mm) tolerance. On the rare occasions that we find tiles that exceed 1/8 inch (3.2mm) deviation from the standard size this is noted in our description. Tiles are more often found undersize than oversize.
Thickness also varies, the standard intended thickness is 3/8 inch (9.6mm) although some tiles were made to be as thin as 5/16 (8mm). Other tiles were made to be 1/2 inch thick, these are usually tiles with a flat surface and taking a cue from 19th century Minton tile catalogues we refer to these as 'hearth quality'. Thickness also varies due to manufacturing conditions. Typical variations in thickness can easily be overcome in fixing to walls by varying the thickness of the applied adhesive. Glazing can also affect the thickness, where tiles were not precisely level in the kiln the glaze may pool to one edge or corner.
Decoration affected the firing conditions and hence the dimensions, the greater the height and/or depth of relief in the tile the more likely there is to be variance from the norm. Some relief tiles were made with a reverse impression of the moulding in the back of the tile to ensure a consistent thickness of body and hence reduce stress in the manufacturing processes. They were also most often used in external architectural situations where the wider range of environmental conditions can greater stress the tiles, C P Sutcliffe and Maws are most noted for such tiles. Colours also affected firing conditions, for example red tiles have a greater tendency to be undersize.
Consistency of dimensions improved as manufacturing technology advanced, pre 1880 variations were more pronounced, post 1910 consistency was very good.
Copeland tiles are quite distinct in as much as tiles designed to be rather more like plaques may be thinner, 1/4 inch (6.4mm) similar to delft tiles, wall tiles are often closer to 7/16 inch. Most Copeland tiles were made of a more durable porcelain like clay.
Minton Hollins and Pilkington tiles are the most true to size though their tiles tend to be less inspired in terms of decoration with more restrained relief and colours.
Tiles also may not be exactly square. T A Simpson appeared to have the most problems in this respect. Tiles also may not be exactly flat.
In fixing we would suggest a skilled craftsman or a capable DIY enthusiast is best suited to the job. A jobbing tiler used only to fixing modern machine made tiles will likely underestimate the time and hence cost of fixing and may be more inclined to cut corners to get the job done according to their estimated time and budget.
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