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Subject: Tests for "lignin-free" materials

Tests for "lignin-free" materials

From: Walter Henry <whenry>
Date: Tuesday, July 16, 1991
First, take a look through the FileList, as there has been some
discussion on lignin in the DistList.

>From the Paper Conservation Catalog outline on Spot Tests
(D.L. Mayer, compiler):

    Begin Quote

    Sensitivity: With the aid of a hand lens, less than 5% of mechanical
    wood fibers may clearly be seen (Grant 1961m 377)

    Results:  A bright- or deep-red or magenta color indicates
    mechanical or semi-mechanical wood pulp, unbleached chemical pulp or
    other lignified fibers such as jute (whether raw or partially
    cooked). Unbleached flax, shive, or hemp shive may also stain red.
    The intensity of the red color gives an indication of the amount of
    lignin.  The tested area remains colorless to pale-yellow (or yellow
    if reagent is old) when no or minimal lignin (less than 5%) is
    present.  If the paper has a small or trace amount of very ligneous
    fibers, the individual fibers stain red and can be seen with a hand
    lens or the naked eye.

    Caution/Interference:  The stain is permanent.  Barks, knotwood,
    clumps, etc. develop a color reaction more slowly; color forms in a
    few seconds to minutes.  Some dyestuffs also give a red color with
    hydrochloric acid (Grant 1961, 377).  The dye metanil yellow can
    turn red with phloroglucinol (TAPPI T401).  A purple color reaction
    indicates the presence of iron (Browning 1977, 318).

    End Quote

                  Conservation DistList Instance 5:10
                  Distributed: Thursday, July 18, 1991
                        Message Id: cdl-5-10-007
Received on Tuesday, 16 July, 1991

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