IDENTIFICATION OF THE FORBES COLLECTION PIGMENTS: I. WHITES
Gary W. Carriveau, & Diana Omecinsky
3 RESULTS AND DISCUSSION
THE RESULTS of our studies are found in Table II. The following information is given:
- column 1: new numbering system (Buck)
- column 2: old numbering system (Forbes)
- column 3: pigment identification attributed to Forbes
- column 4: our pigment identification and JCPDS File Card No.
A dagger (†) denotes samples where x-ray fluorescence was used to assist x-ray diffraction pattern analysis.
For a number of pigments, there are significant differences between Forbes' identification (column 3) and our own.
The results in column 4 are complete except for two samples (1.05.2 and 1.05.5) that we were unable to obtain. In fact, our original collection of Forbes pigments contained only 39 of the white samples. It was only through the generous assistance of other museums and institutes that our collection is as complete as it is at this time. We would like to request further assistance from anyone having the missing Forbes pigments.
The following samples require additional comment since the XRD and XRF analysis gave inconclusive results.
3.1 Samples 1.02.5 and 1.02.9
The XRD pattern was taken using normal sample size; however, no discernable pattern other than the diffuse background was obtained. XRF provided qualitative elemental information as follows:
- sample 1.02.5 contains K, Na, Al, Si
- sample 1.02.9 contains A1
3.2 Sample 1.02.4
Identified by Forbes as Fullers Earth, gave XRD results indicating impure Si02. Fisher Scientific provided an analysis of their commercial Fullers Earth; it contains 64% SiO2, 16% Al2O, and oxides of Mg, Mn, Ca, Fe, Ti and Na.
3.3 Samples 1.10.3 and 1.20.5
The XRD patterns showed d-spacings similar to the general reflections characteristic of unoriented iron-rich montmorillonite. XRF data confirmed the presence of Fe and lack of K, which makes the sample dissimilar to the muscovites. The main difficulty in the identification of these two samples is that x-ray identification is not the best method for untreated and, therefore, unoriented clay mineral samples, especially montmorillonites.6
ONE AUTHOR (Diana Omecinsky) wishes to gratefully acknowledge the financial support of the Andrew W. Mellon Foundation. We also thank Gary Alden, Mary Calisto, Eugene Farrell, Thom Gentle, Michael Heslip, Laura Juszczak, Richard Newman, Philip Vance, and John Winter for their help in supplying Forbes pigment samples and information about the collection. We wish to thank Marta Baranyk and Richard Caldwell for their assistance in taking XRD data. We express our thanks to Jerri Nelson, Eugene Farrell, Christopher Tahk, and anonymous referees for their helpful comments and suggestions on this manuscript.