Patination

Patination is a general term for visible chemical alterations of exposed surfaces. In the present context, it refers primarily to the tendency of flaked surfaces on lithic artifacts to alter in color after prolonged exposure to air, sunlight, soil, and water. Patination is of interest archaeologically as a potential indicator of the relative or absolute age of the surfaces.

Malcolm J. Rogers (1929:461, 1958:2-3, 1966:33) attached considerable value to patination as an indicator of age. He reported that San Dieguito and Late Prehistoric volcanic artifacts could be distinguished by the absence of patination on the latter.

Dennis H. O’Neil (1982:125-130) considered patination to be useful in evaluating the chronology of site SDM-W-1556. In addition to looking at relative patination as a broad indicator of relative artifact age, he noted the presence of artifacts with different degrees of patination on different flake scars, which evidently indicated that tools or cores had been recycled after an interval of discard.

A cautionary note was added by Richard H. Norwood (1980). In excavations at a Rancho Santa Fe site, Norwood recovered the two halves of a large biface. The fragments came from separate excavation units and different depths, and the two fragments had strikingly different degrees of patination. He concluded that the case “demonstrates that differential patination cannot be used with any degree of reliability to assign relative dates to artifacts, even when they occur in the same site and are made of the same material” (Norwood 1980:176).

For patination to be used to infer absolute or relative age, several factors evidently will need to be controlled:

• The specific rock type involved needs to be held constant .
• Comparisons should preferably be made on materials from similar depositional contexts. Heat, moisture, exposure, and soil chemistry may all be factors of significance for patination rates.
• To evaluate the degree of patination on a specimen, it may be necessary to break open a fresh surface in order to verify the interior rock color.
• Some replicable standard for making interassemblage comparisons on the degree of patination, beyond a subjective “light,” “medium,” or “heavy,” may be desirable, for instance through the use of standard color measurements on fresh and patinated surfaces. 

PROSPECTS

Future archaeological investigations may be able to determine whether patination can be used reliably as an index of relative or absolute age. They may also be able to identify the factors that may have to be controlled for such use to be successful.