Watercolors

Following my posting in Conservation DistList Instance: 14:62
Tuesday, May 15, 2001:

>We would like to know if anybody has done any aging tests on current
>Winsor and Newton watercolors. We are using them for inpainting and
>we are concerned by their light fastness. We could get only general
>information on their stability overtime and are particularly
>interested in obtaining further details. We wish to know specific
>color changes recorded after stated length of time and conditions
>under which the experiments were performed.

We got the answers we were looking for from the Winsor and Newton
Chief Chemist Alun Foster:

   "Lightfastness testing is according to ASTM D5067 for
    watercolours using test method D4303 to a total radiant dose of
    1260 MJ/m2 in a xenon arc lamp.The relative humidity of the test
    is set at 55+/-5%. We do not carry out specific humidity
    testing. Any fading is measured in terms of CIElab Delta E*ab
    with less than 4 being lightfast I and 4 to 8 lightfast II.
    Winsor and Newton permanence ratings are somewhat tighter in
    that only colours which have known history of chemical stability
    over centuries has the highest AA rating, these are mostly
    natural inorganic pigments such as earths or synthetic inorganic
    pigments such as cobalt mixed oxides. Most other pigments in
    ASTM I and II are in Permanence A."(2/13/01)

Since we are using AA watercolors for our inpaintings, we asked for
the result of there color change after testing. We were
particularly interested to know if any of the colors were going to
get darker over time. Alun Foster replied :

   "Colours are tested according to ASTM D 4303 (Xenon arc) as
    graded washes. Most of the colours listed showed no change over
    the exposure specified. Slight fading occurred with Lemon Yellow,
    Winsor Red, Permanent Carmine, Prussian Blue and Indigo in
    weaker part of wash. No colours showed darkening. "(5/22/01)

We are now going to use the following colors for inpainting:

        431 nickel titanium yellow
        192 cobalt violet
        180 cobalt blue deep
        178 cobalt blue
        137 cerulean blue
        692 viridian
        637 terre verte
        187 cobalt green
        425 naples yellow deep
        744 yellow ochre
        522 raw sienna
        074 burnt sienna
        678 venetian red
        317 Indian red
        554 raw umber
        076 burnt umber
        676 Vandyke brown
        609 sepia
        331 ivory black
        150 Chinese white

We would like to thank Alun Foster, Chief Chemist of Winsor and
Newton, David Pyle and Laurie Hines from Colart Americas, who
contacted Alun Foster for us.

Valerie Lee
Assistant conservator
Freer Gallery of Art and Arthur M.Sackler Gallery
Smithsonian Institution
Washington DC 2056-0707


                                  ***
                  Conservation DistList Instance 15:6
                  Distributed: Tuesday, June 26, 2001
                        Message Id: cdl-15-6-001
                                  ***