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Yellow color disappears.

edited February 14 in Painting
Hello everyone!
I noticed that yellow color (that is cadmium  yellow) disappeared after drying the painting at 200°F for 30min. Did anyone ever have this issue?

Here is how my painting looked like before drying:
... and here is how it looks like now after the heating: 

I cannot explain this. The leaves at the lower-right corner almost have not changed in color. Strange. I called it The ladybug effect.  Hope someone can explain this...

Comments

  • MyArtsClub

    This phenomenon is called thermochromism.

    Heat and/or light will accelerate the deterioration of fugitive colour such as hansa yellow.
    Curiously cadmiums were introduced to avoid this problem.
    I have no explanation why some leaves changed and some were stable.

    Expert opinion on accelerated drying advises not to exceed 100f.

    Denis


    MyArtsClubBOB73
  • edited February 14
    Thank you Denis. I did not know that... Do you think the original color can be restored by glazing yellow paint over? 
  • edited February 14
    A yellow glaze should work.  Alternatively, you could repaint the leaves that have turned blue opaquely. Either way, let it dry naturaly then  varnish as usual. 
    MyArtsClub
  • I think you over cooked it and way to fast - accelerated drying time does not work with oils.
    It look a great painting by the way, certainly worth fixing
    MyArtsClub
  • it's a beautiful painting i'm sure you'll be able to fix it with glazing.  just wondering - the paint  film didn't crack or peel after that temperature?
    MyArtsClub
  • edited February 14
    Yes, I know I am crazy enough to experiment like this without doing a research or asking more experienced people :). Anyhow, I fixed it really easily.  Yellow glazing worked out well. After that I simply refreshed some details and overpainted some areas with darker green color. 

    @ArtGal no, it did not crack. It has dried significantly, though not completely and may be that's why it did not crack. Here is how it looks like after all these turmoils.
    Thank you all for really helpful discussion. I'll let it dry some more time at 100F and then overglaze some color reflections here and there on the petals.   

  • Oh, I forgot to ask - Don't  yout think the roses look somewhat flat? May be I should add some dark tone in the shadded areas and lighten the highlights?..
  • I think those white roses wouldn't have grey shadows, but reflected light from their surroundings.
    MyArtsClub
  • What brand of cad yellow? Can you look on the paint tube and see what the pigment number is and share?
  • I don't think they look flat, i think you will see after you glaze the petals. and then  you  add darks if needed 
    MyArtsClub
  • @CJD , interesting question. I had a few tubes containing yellow paint and combined them together to make a larger stock of about 50% cadmium yellow, 25% Lemon yellow and may be some cadmium yellow hue. I discarded the empty tubes, so not 100% sure though.

    Next. I placed the canvas into the oven so that the upper side of it (where the bleached leaves are) was deeply inside. I opened the oven several times to check how it was going and probably cooled the lower part of it somewhat. That is why, I guess, the leaves at the bottom did not bleach much.

    After that I made an experiment to test if the temperature of 200F can bleach my yellow paint. For that, I painted several colors on two paper pieces and placed one in the oven while keeping the other one at ambient temperature. After 30 minutes in the oven, the yellow paint (#1) did not bleach at all. The green mix (#5) also did not change. May be just a little..  So, the mistery is still unresolved to me. 

  • White roses are very reflective and transparent.  You need to darken in shaded areas and touch some surrounding color into the roses.  I would use a greenish grey color in the shadows and see how that looks.  Lovely set up.
    MyArtsClub
  • MyArtsClub

    Looks like the heat is changing the crystalline cadmium sulphide to the amorphous and colourless cadmium sulphate. The heat treatment leaves the blue unchanged.

    It is well known that cadmiums are not lightfast for outdoor applications. It is known that CdS exposed to water and light turns into colorless cadmium sulfate. Generally, if a pigment cannot survive outdoors, that should be a warning flag that its long-term permanence is suspect even indoors.

    http://www.wetcanvas.com/forums/archive/index.php/t-1390481.html

    The mixture of yellows may include an azo, hansa, or a hue of non cadmium pigments, accounting for the variation in heat response.

    Denis

    MyArtsClub
  • CJDCJD -
    edited February 18
    The author of that quote was wrong about hansa yellow being superior to cadmium yellow. Williamsburg recently discontinued their Hansa yellow line after it scored poor for lightfastness in their most recent tests. Cadmium yellow is the best yellow you can use (along with Mars yellow and yellow ochre). Ideally use a good brand of it like Williamsburg or Rublev and don't mix it with less stable and lightfast yellow pigments.

    Saying hansa yellow is likely more lightfast than cad yellow is an odd claim for someone to make, and stating that cadmiums lack long term performance is absurd. 
    PaulBMyArtsClubtassieguy
  • Which hansa yellow? There are a whole range of pigments under that name.

    I know they have brought in replacements for PY3 and PY73 in their acrylics.
  • edited February 18
    I don' t know about lightfastness, @Dencal,  but who would hang an oil painting outdoors in the weather and sun. Nothing would be archival in such conditions    For those situations one would use outdoor house paint and even that needs redoing regularly. I may be wrong but for fine art painting we can probably rest easy with the cadmiums.  :)
  • Rob

    My focus was trying to solve MyArtsClub question about the disappearing yellow. I was not defending, attacking or promoting the use of cadmium. It is the best of a fugitive bunch of pigments.

    But since you ask

    but who would hang an oil painting outdoors in the weather and sun. 
    Sign writers, silo artists, muralists, fresco painters, advertisers, billboard artists, graffiti artists, house painters, ... all use cadmium pigment in some form.

    Denis


  • It's too low in chroma, but transparent Yellow Iron Oxide is the most lightfast yellow pigment.
  • CJDCJD -
    edited February 18
    @Richard_P I don't kow which hansa yellow pigment Williamsburg was using, but apparently all organic pigments are currently suspect as the testing done to determine their rating was done with only a couple samples each. Manufacturers all now know that a pigment from one source may be lightfast but the same pigment from a different source may not be. Mixing the same pigment with a different white can also make a huge difference. Golden gambin and Natural pigments are working together now to retest all organic pigments they use. Data should be available in the next 3 years.

    Other manufacturers know about this but have decided not to participate so I am boycotting all of those brands :) it's crazy they are perfectly fine stamping the astm I rating on all their paints despite knowing they might not be lightfast.

    Golden/williamsburg has already posted some info on some pigments on their site. Hansa yelllow was one of them
  • @CJD Can you post the sources for this so I can read about it?
  • This is mostly it, although george o hanlon has made another comment or two in the FB group. Interesting stuff! 

    I'm doing my own test strips of all my pigments mixed with lead white and on my south facing window. I'll post results whenever significant fading is visible in some of the samples.

    https://www.naturalpigments.com/artist-materials/pigments-artists-paint-lightfast/
    MyArtsClub
  • Thank you. Interesting!
  • The real, deadly effect can give Magnesium content into filler in combination with acidic content and oxygen. Cadmium Acetate/Oxalate + (SO4) + Mg2+ = (MgSO4·7H2O)
    (MgSO4·7H2O) is extremely hygroscopic and it is always present in a water solution into oil paint film. The water solution of magnesium sulfate will destroy all Ultramarine paint structure into non-adhesive flakes. (Ultramarine is also sulfuric-content pigment) It can also destroy all cadmium paint layers and will cause it's deadly chemical discolorations. Such modern Ultramarine paint can degrade during only several years. Thinking about these deadly degradation processes into contemporary art, I just found, that the presence of Lead White can prevent deterioration because Lead Sulfate is not soluble.
    MgSO4+PbO+CO2=PbSO4 (insoluble) + MgCO3 (insoluble)
  • edited February 18
    I was thinking, may be magnesium sulfate (or other chemicals..) is present in gesso used to prime my canvases. Just a thought. That can explain why yellow paint faded only from canvas but not from paper used to test it. 
  • You are a terrific artist but not very good at baking.
    MyArtsClub
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