A Scanning Electron, EDX and Microscopic Study of the Forbes Pigment Collection

June 7, 2005

by Frank Hengemihle
Preservation Directorate, Research and Testing Division

INTRODUCTION

The Library of Congress, Conservation Division of the Preservation Directorate has a collection of Pigments. The Forbes Collection of Pigments - not all pigments on the contents list are present. This study is an effort to subject each of the samples to SEM/X-ray microanalysis and light microscopy for the following purpose. 1. Building a collection of samples on SEM Aluminum pin mounts. 2. Collecting X-Ray spectra of each sample. 3. Photographing each sample with an electron and light microscope to produce an album of pictures.

MATERIALS AND METHODS

Aluminum Pin mounts were etched with numbers, scotch tape was used to clean the mount of debris from the etching. Carbon tape was applied to the aluminum mount but the teflon protective cover of the tape was not removed until immediately prior to the sample application. The contents list was used to order the pigments which were numbered starting with 1 for the first pigment on the list in the collection. A wooden cue tip was used to get the sample. The wooden end was used to lift the sample out of its glass container and place the sample on the carbon tape. The cue tip was disposed of after a single usage. The teflon which was pulled off just prior to applying the sample was used to press the sample into the carbon tape.

The S-200 Cambridge Scanning Electron Microscope was employed to view the samples. The Kevex Sigma system was used to get the X-ray Spectra and to produce the digital images. For producing the X-ray Spectra magnification was set at 1,500 X, the deadtime was held at around 35% or a 5000 count rate, the Accelerating Voltage was 25KV.

RESULTS AND DISCUSSION

The pigment list is in order by color. There are 10 sections of color which the collection refers to as codes. Each of the colors is subdivided by a grouping mechanism. Finally a third section of the sample number refers to the individual sample bottle, e.g. 1.06.8 - Here the 1 is for the color white, the .06 refers to zinc whites. The .8 refers to a specific sample Permanent Chinese White.

There are 10 codes or colors: 1 - White, 2-Black, 3-Yellow, 4- Brown, 5-Orange, 6-Red, 7-Violet, 8-Blue, 9-Green, 10-Clays or unidentified.

Code 1 is White. 1.01 is white containing calcium. 1.02 is Aluminum compounds. 1.03 is Magnesium Compounds. 1.04 is Silica Compounds. 1.05 is Lead Whites. 1.06 is Zinc Whites. 1.07 is Barium Whites. 1.08 is Antimony Oxide. 1.09 is Titanium White (after 1920). 1.10 is "unidentified". 1.20 is oriental Pigments. - Note: For code 20 "No attempt is made to classify pigments as to mineral or organic sources because information is lacking. The 20 Code signifies Japanese or Chinese only. Thus 3.20.4 may be a yellow ochre, though it is not coded 3.04.x."

There are 18 samples listed in code 1.01 - White, Calcium Compounds. The sample box contains eight of the 16: 1,9,12,13,14,15,16 and 18. Spectra of the samples and a digital image captured using the Kevex Sigma Ultrascan software are presented below. Light microscope photographs are from the Zeiss system.

Sample 1: Sample 1 is a white powder its contents list designation is 1.01.1 or in the old system 132. The sample is "Gypsum from Alabaster, (terre Alba), CaSO4.2H2O Munich EWF".