JAIC 1987, Volume 26, Number 1, Article 3 (pp. 27 to 44)
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Journal of the American Institute for Conservation
JAIC 1987, Volume 26, Number 1, Article 3 (pp. 27 to 44)


Martha Goodway


BrunoLuniak, Identification of Textile Fibres. Qualitative and Quantitative Analysis of Fibre Blends, London1953, p. 123; A.Herzog, Textile Forchung4 (1922):58.

R.Mauersberger, editor, Matthews' Textile Fibers, sixth edition (New York1954).

Mary ElizabethKing and Joan S.Gardner, “The Analysis of Textiles from Spiro Mound, Oklahoma”, in Anne-Marie E.Cantwell, James B.Griffin, and Nan A.Rothschild, editors, The Research Potential of Anthropological Museum Collections, Annals of the New York Academy of Sciences376 (1981):123–139.




LUNIAK, FOLLOWING HERZOG, suggested the possibility that the direction (right- or left-hand) of cellulose could be determined optically using a polarizing microscope.1 Specifically, he states:

For the differentiation of flax and hemp fibres their opposite behaviour in polarized light between crossed Nicol prisms after insertion of a selenite plate Red I in the 45 position may be noted. Flax fibres display addition colours when parallel to the plane of the polarizer, and subtraction colours when at right angles; hemp fibres vice versa. A part of the fibres may be neutral; in general the differences are not so pronounced with hemp fibres. Comparison with known samples is advisable.

In order to put this suggestion into practice it is necessary to have a polarizing microscope with a compensator slot and a first-order, so-called red plate. Actually, the color of the field of view when the polars are crossed and the red plate is inserted in the compensator slot may be more accurately described as magenta. It is more convenient if the microscope, as do most polarizing microscopes, has a rotating stage.

Since bast and leaf fibers are polycrystalline they do not behave optically as neatly and unequivocally as a single crystal, and complete extinction under crossed polars does not occur in these fibers. For this test an individual fiber is more likely to give a definite response than a bundle of fibers, but not all individual fibers are good subjects. Colors under the red plate often cannot be observed when the fiber is in the 45 position which gives maximum brightness under crossed polars alone. To yield diagnostic colors when the red plate is inserted, the fiber should be observed first under crossed polars in a “nearest-to-extinction position” (since they do not extinguish completely) of 0 or 90 that is, the fiber should be parallel to the optical direction of either the polarizer or analyser. Rather than as an extinction position, this might be described better as the position in which the fiber appears most gray, or darkest.

The fiber to be identified must be observed first without the red plate in order to locate exactly an area of the fiber most nearly totally extinguished by crossed polars (Plate 1). When the red plate is inserted, areas that were black under crossed polars become either yellow or blue (Plate 2). If the stage, with the slide, is then rotated 90 the other color should appear, blue where it was yellow or yellow where it was blue (Plate 3). The colors depend on the orientation of the polarizer, the analyzer, and the red plate. Therefore each time this test is used, the orientation of the optical elements should be determined by using a comparison standard known to be flax. A left-hand fiber will give the same colors but each in a direction 907deg; from that or flax or ramie. In some cases the color shift will not be very distinct. That is why locating those areas of the fiber which are darkest under cross polars before the red plate is put in, and using only those areas for identification is so important.



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Copyright 1987 American Institute for Conservation of Historic and Artistic Works