A mean ceramic date offers a quick and rough indication of the chronological position of a ceramic assemblage (South 1977). The mean ceramic date for an assemblage is estimated as the weighted average of the manufacturing date midpoints for the ceramic types found in it. The weights are the frequencies of the respective types in the assemblages. Types represented by more sherds have greater influence in the calculation. Manufacturing midpoint estimates, and the beginning and ending manufacturing dates from which they are computed, come from documentary evidence on the ceramic industry.
In DAACS, we offer two types of Mean Ceramic Dates. The first, found on the Chronology pages for individual archaeological sites, are generated using traditional ceramic ware types such White Salt Glaze, Chinese Porcelain, and American Stoneware. The manufacturing date range for each ware type was assigned using traditional documentary sources (e.g. Noel Hume 1969, Miller et al. 2000). A complete list of DAACS ware types can be found in the sidebar on the right.
The second type of Mean Ceramic Dates, mean-ceramic-date types (MCD types), are used to generate the dates produced by the Mean Ceramic Date Queries. MCD-type dates are based on ceramic types whose manufacturing spans can be narrowed based not only on ware type but also on decorative technique and applied color. DAACS MCD types are based on the intersection of three dimensions of variation: Ceramic ware (e.g. Creamware, Pearlware, Delft), decorative technique (hand painted, transfer printed), and applied color. Color is measured using the DAACS Munsell Color Range system (see MCRS in About the Database). DAACS staff tabulated all unique combinations of ware, decorative technique and applied color that occur in the DAACS ceramic table. Each unique combination was assigned to a MCD type, based on documentary sources (e.g. Noel Hume 1969, Miller et al. 2000, Sussman 1997). A complete list of DAACS MCD types and the mode combination mapped to them can be found in the sidebar on the right.
The DAACS database records decorative technique and applied color for individual decorative elements. Different decorative elements on the same sherd may belong to different MCD types. Sherds with multiple elements are assigned to the single MCD type having the shortest manufacturing span.