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MITRA Forum Question Details

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  • oxidation of metalpointsApproveRejectUn-ApproveSubscribeUn-Unsubscribe
    Question asked 2017-05-14 17:00:13 ... Most recent comment 2017-05-21 19:31:33
    Drawing Materials Grounds / Priming Egg Tempera
    Question

    I sometime expose my metal point drawings to sulphur (by placing them under a "tent" alongside an open jar of liver of sulphur) to speed up the oxidation and darkening of the drawing.  Does exposure to sulphur cause any detrimental affects to the materials of a metalpoint drawing (to either a paper or wood-based panel support; or to an acrylic or traditional gesso ground)?  Are there other recommended ways to speed up oxidation?  I had a cohort once tell me he sips whiskey while drawing and blows on his images - any truth to his claim that this speeds oxidation?  

    By the way, which is correct: metalpoint?

    Koo Schadler

Answers and Comments
  • EditDeleteModerator Answer

    I cannot answer all of these points but will weigh in on what I can and send the others on to others. First as to terminology, my resources say one word: metalpoint. As to your question about the use of whiskey to speed up oxidation. I do not believe that this would have any real contribution. The ethanol portion would be reactive to the metal than plain water. I do not believe that any components in the oak casks associated with aging the Whiskey would reach the metal but I guess that perhaps the tannins could theoretically have a tiny effect, but I doubt it. Others may have opinions that are more concrete on this. I hope that some of our paper conservators and scientists can comment on your other points.

    BTW, you would probably have interest in this recent publication.

    https://www.archetype.co.uk/publication-details.php?id=239

    Brian Baade
    2017-05-14 17:21:33
  • EditDeleteModerator Answer

    ​Hi Koo, I don't believe that short-term exposure to liver of sulphur (a varying mixture of potassium sulphides) would necessarily cause any detrimental effects to a paper-based support; in fact, liver of sulphur was used to tone black and white photographic prints around the turn of the 20th century.  Due to the fact that this substance is alkaline, I also don't think that short exposure would be problematic for an acrylic ground.  I'm not sure how it might affect a wood-based panel support - perhaps someone else could weigh in on that one. 

    Gillian Marcus
    2017-05-15 14:50:11
  • EditDeleteModerator Answer

    ​There is so much to think about, here. I don’t know whether Ag2O looks different that Ag2S, but I think that sulphur is never a good idea.  I wonder whether the Ag2S would be stable, or could continue to react, with atmospheric gases. I think that the sulphur would be bad for the paper, and may react with the acrylic, in either sheet or dispersion. Ultimately, I think that keeping thing as chemically simple as possible is always the best path to stability. If enhanced oxidation is really needed, I would be least uneasy with exposure to H202, since it brings only H and O, to the party, but it would have to be in a gaseous form, for my comfort, and I have no ideas whether this might work. Blowing on the image would bring it CO2 and any biologicals that might be expectorated, with the blows, and I would imagine that all would probably be a source of oxidation. 

    Hugh Phibbs

    2017-05-15 16:00:19
  • EditDeleteModerator Answer

    While I do not know with absolutely certainty, I suspect that hydrogen sulfide (that rotten egg smell) evolves from by a liver of sulfur solution.  Hydrogen sulfide is a common ingredient in air pollution.  As an oxidizing agent, it is corrosive – which is why it tarnishes the silver in metalpoint drawings and darkens lead white pigments (now prohibited for artist's use).  Conservators see darkened lead white (lead carbonate converted into lead sulfide, usually resulting from exposure to air pollution or the VOCs emitted from plywood) pigments quite often in old master "heightened" drawings, in illuminated manuscripts, and, also, around the edges of the preparatory grounds for metalpoint drawings. However, oxidizing agents also attack the double bonds of cellulose, accelerating the symptoms of paper aging, such as brittleness and yellowing.  As a paper conservator, I cannot recommend the exposure of paper to hydrogen sulfide.  At the same time, we do not know how much exposure to hydrogen sulfide (how long, what concentration) is required before meaningful (greater or faster than "normal") degradation takes place. So a pragmatic approach would be to expose the drawing until you get the results you want and use a good quality, sufficiently sturdy, and toothy paper as the support for the preparatory ground.  

    As to why whiskey breath would accelerate tarnishing of silver, I cannot say – must have been something he ate!

    - Margaret Holbein Ellis

    2017-05-15 19:20:44
  • ApproveRejectUn-ApproveUser Comment

    I expose my drawings to sulfur for only a day or two, no more - it's sufficient to make a perceptible change in tone and color, but hopefully not enough to affect support or ground (my support is generally a wood-based panel, which I would suppose is more resistant than paper to detrimental effects, yes)?  I'll see what it's like to put Hydrogen Peroxide on an image (I know, Hugh said only in gaseous form, but I'm game to try spritzing it on a test panel to see what happens). Thanks for all the helpful replies, and if any other ideas come up for accelerating oxidation of metalpoint, I'd be interested. 

     

    Koo Schadler

    2017-05-17 10:23:17
  • ApproveRejectUn-ApproveUser Comment

    An update - I spritzed Hydrogen Peroxide onto some silverpoint marks and it dissolved them, they lifted right up.  I've had success minimizing metalpoint marks with rubbing alcohol on a cotton swab; seemingly HP does the same thing, but I'm not sure if there is a detrimental effect to the ground.

    I then placed a panel with silverpoint marks face down over a tray of Hydrogen Peroxide, so the marks were exposed just to the fumes. They turned from grey to brown in 24 hours, although the value of the marks did not deepen.

    Koo

    2017-05-21 10:00:01
  • EditDeleteModerator Answer

    ​Thanks for the update Koo...

    Kristin deGhetaldi
    2017-05-21 19:31:33
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