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MITRA Forum Question Details

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  • Extreme dilution of paints on absorbent surfacesApproveRejectUn-ApproveSubscribeUn-Unsubscribe
    Question asked 2017-04-20 20:05:55 ... Most recent comment 2017-04-24 11:01:00
    Acrylic Watercolor Gouache Egg Tempera

    ​From what I know, there is no limit to how much watercolors can be diluted when painted on paper. I was wondering if the same can be said of all the other water-soluble paints. Is it okay (in terms of durability of the finished work) to dilute:

    1. Acrylics
    2. Gouache
    3. Tempera (egg and non-egg)
    4. Inks

    as much as one wants if painting on an absorbent support, like paper? I read that the absorbency of the fibers ensures that the pigments are trapped within the piper, so there should be no conservation issue in that regard. Is that true?

    Also, should such works be varnished, and if so - with what?

Answers and Comments

  • EditDeleteModerator Answer

    The stability of lean paints created by over-diluting aqueous binding media is tied to the absorbency of the support. As you state, the more “open” the network of fibers in the paper support, the better off you will be. One simple way to test whether or not your artwork might face problems in the future is to gently rub the surface of the painting using a soft cloth after it has dried. If a substantial amount of color comes up then the painting is indeed under-bound and there may be preservation issues.  However, if only a very minor amount of pigment comes up then you may be able to get away with your system as long as the piece is properly protected from abrasion (and during transportation and handling) so framing would be key here. One thing to note is the lightfastness of the pigments you are using. To a certain extent, the binder plays a protective role in slowing down or even inhibiting unwanted fading/color changes. Obviously, with the pigment-to-binder concentration at the level you are considering working at, there would be a minimal amount of binder. This can be an inherent problem with media like watercolors/gouache, which is why many museums display these works at subdued light levels. So again, looking into UV-protective glazing might be worthwhile here.

    As far as varnishing goes, this is really an aesthetic decision. Varnishing a lean paint film like one you suggest would create a relatively matte, undersaturated color effect. Varnishing would drastically darken and saturate such paint. This effect would be rather permanent as well as it is difficult to completely remove varnish from a very matte “thirsty” surface. A thin spay fixative may create less of a color change. Unfortunately, we cannot endorse many of the proprietary fixiatives available, as we do not know precisely which resins they use. I do think that B-72 is a good resin for this purpose. The availability of B-72 in a spray can in discussed in this MITRA thread:

    It is possible that fixatives offered by Krylon or other brands are fine (they probably consist of acrylics that are stable for the most part). No matter what you choose, please record your painting methods and materials choices somewhere on the reverse of the piece, or the frame, so future owners and conservators are aware that it was the artist’s decision to varnish the work, NOT a dealer or someone else down the road.

    Kristin deGhetaldi and

    Brian Baade
    2017-04-21 13:47:15
  • ApproveRejectUn-ApproveUser Comment

    Thank you for the detailed answer.

    Am I right to assume that pigments with an ASTM rating of I or II, or a high Blue Wool Scale score (7-8) should remain lightfast even without the binder?​

    As for the picking up of colours - I don't assume anyone will be cleaning works on paper with a damp cloth, but would it make sense to coat the finished work with diluted PVA to provide a protective barrier?

    2017-04-21 15:09:13
  • EditDeleteModerator Answer

    ​As far as ASTM (I being excellent, II being good, and so on) ratings go, yes, the binder and presumably the AMOUNT of binder matters. I include an excerpt from our "ASTM and Lightfastness" document in the Resources section here:

    It is important to note that the lightfastness of a particular pigment can differ with the vehicle used. For example, Vermilion has a lightfastness rating of I (excellent) when mixed in oils and acrylics. However, in a watercolor vehicle, it has a rating of III (fair). For this reason, one should check the lightfastness rating for both the specific manufacturer and the medium.
    PVA would probably be fine as well...but be sure it is a pH neutral PVA resin. And while no one (presumably) would be cleaning your works with a damp cloth, realize that paper conservators bathe prints and drawings all the time but ONLY after extensive testing is carried out on pigmented areas to determine stability. This is done routinely to rid the paper of yellowed/discolored material associated with acidic fractions that can form within the paper substrate as it ages, to diminish the appearance of tidelines should the work of art come into contact with moisture and/or a liquid substance, and then there is local application of moisture/aqueous cleaning agents that is done to remove mold growth or stains. If any color comes up during testing the work of art is essentially declared too fragile to clean and may not end up getting selected for an exhibition, etc, etc. But if the work is properly stored, framed, and notated on the reverse it should fare uch better in the future.

    Kristin deGhetaldi
    2017-04-21 16:43:04

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