Canadian Historic Sites: Occasional Papers in Archaeology and History No. 16

The Western European Coarse Earthenwares from the Wreck of the Machault

by K. J. Barton

Appendix B. Thin-Section Examination and X-Ray Fluorescence Analyses of Ceramic Sherds from the Machault.

by R. J. Traill.

Six coarse earthenware ceramic sherds recovered from the Machault were examined. The sherds, numbered 1, 2, 3, 4, 6 and 7, were primary examples of the ceramic categories into which K. J. Barton divided the coarse earthenwares from the Machault. Sherd No. 1 was from Barton's Type 1; sherd No. 2, from Type 2; sherds Nos. 3 and 4, from Type 3; sherd No. 6, from a red-fabric plate with "circles of dots" decoration (Miscellaneous No. 1), and sherd No. 7, from a white-slipped redware dish with applied green colour decoration (Miscellaneous No. 3).

Thin sections were prepared to show cross-sections of the sherds and these were examined under a petrographic microscope. All the sherds were found to have a simple mineral composition, consisting of angular fragments of quartz, with a small amount of feldspar and mica in a fine-grained matrix of undetermined mineral composition. X-ray diffractometer powder patterns confirmed the simple mineralogy: sherd No. 1 (Type 1), major quartz, minor alumina; No. 2 (Type 2), major quartz, trace alumina and feldspar; No. 3 (Type 3), major quartz; No. 4 (Type 3), major quartz, trace alumina and feldspar; No. 6 (Misc. 1), major quartz, trace feldspar, and No. 7 (Misc. 3), major quartz, trace feldspar.

The textures observed in thin section fall into four categories.

Sherd No. 1

Very fine-grained matrix containing relatively few randomly oriented fragments of angular quartz. Most of the fragments are smaller than 0.02 mm. and only a few are larger than 0.05 mm.

Sherd No. 4

Contains abundant quartz fragments in a very fine-grained matrix. The fragments are well-sorted as to size and most fall within the 0.02 mm. to 0.01 mm. range. Many of the fragments are elongated and show a preferred orientation parallel to the surface of the sherd.

Sherd No. 3

Contains relatively few angular quartz fragments set in a fine-grained matrix. The fragments are very poorly sorted as to grain size and vary from less than 0.05 mm. to more than 0.4 mm. The fragments tend to be elongate and show some preferred orientation parallel to the surface of the sherd.

Sherds Nos. 2, 6 and 7

Characterized by abundant, poorly-sorted quartz fragments ranging in size from less than 0.01 mm. to more than 0.5 mm. The fragments do not show any preferred orientation.

Results of partial semi-quantitative X-ray fluorescence analyses of powdered examples of the six sherds, expressed as percentages of the oxides, are shown in Table 1. The silica/alumina values are of considerable interest as indicators of the composition of the raw materials and suggest three or four different source materials: sherd No. 1, low silica/alumina, 2:3; sherds Nos. 3 and 4, medium silica/alumina, 3:4 to 3.5; sherds Nos. 2 and 7, high silica/alumina, 4:6 to 4:7, and sherd No. 6, highest silica/alumina, 5:2.

Sherds Nos. 2 and 7 showed a common feature that was not present in the other sherds. Both of these sherds have had slip, a thin layer of fine-grained clay, applied to their inner surfaces before firing and glazing. The layer of slip is very uniform, 0.1 mm. to 0.15 mm. thick, and similar in appearance to the material of sherd No. 1. Table 2 shows the results of electron probe microanalyses, expressed as weight percentages, of the matrix of sherd No. 7, the slip of sherd No. 7, and the matrix of sherd No. 1. These analyses confirm the similarity in composition of the two fine-grained clay materials.