Comment by PetitPrince

Daub a day ago

> I wonder whether it's still worthwhile to replaced a yellowed varnish varnish on old painting, just to be sure that it doesn't degrade further (with the assumption that historical varnish are somewhat lesser than modern one, which I really don't know if it's the case).

I would say that we should just live with the difference. There is a near guarantee that our experience of paintings as they exist today will always be significantly different to how they would have been experienced when they had been made, regardless of what we do. The factors are:

- Yellowing of oil/pigment/varnish. This is pretty much inevitable, even in modern paints.

- Fugitive colors. Most high-color pigments tended to fade significantly over time. Degas was once seen crying in front of a Delacroix, upset at how badly the colors had faded, even in his lifetime (It might have been Manet... can't locate the relevant anecdote online).

- Excessive varnishing. It used to be so that paintings received regular varnishing by their owners. Over time, the layers of varnish would build up to a ridiculous degree.

- Lighting. For me this is probably the most annoying factor. A general rule is that paintings should be lighted in the same light that they were painted. The values go to hell if a painting is lighted too brightly. There are many so-called hanging experts, who always light too strongly, even in respected national collections.

Semi-related anecdote: The first time I went to the Rodin museum I was struck by how badly one of the busts had been lighted. Whilst the guards were not looking, I moved it to a more agreeable position. I came back one year later to find it was still in that position.

As for using modern varnishes... I am not expert, but AFAIK one factor that accounts for the amazing longevity of old paintings was the compatibility between their many layers. The canvas, the primer, the paint and the medium were all derived from the same plant: flax. On top of that would sometimes be laid stand oil, again derived from flax. If this continuity is broken, all manner of problems might arise, most of which would be long term issues such as cracking and flaking.

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masklinn a day ago

> AFAIK one factor that accounts for the amazing longevity of old paintings was the compatibility between their many layers. The canvas, the primer, the paint and the medium were all derived from the same plant: flax.
AFAIK that's largely untrue in the general case:
- Canvas painting only appeared in the 15th century, and took a while to spread, paintings before the 17th century (16th in some locations) tend to be on wood panels e.g. raphael and da vinci painted almost exclusively on board.
- Canvas is almost always coated with gesso which at the time would use rabbitskin glue as binder, no flax there.
- While flaxseed was the most common drying oil (in europe), walnut, poppyseed, and safflower, were also in use. And additives were usually mixed in to manage the viscosity of the paint, so even in the "best" case it's not like the paint would be just pigments in linseed oil unless it's a very early oil painting, which wouldn't have been on canvas.
- As for varnishes, not only was flax not the only drying oil for oil varnishes, varnishes could also be "spirit" varnishes (with a resin dissolved into a solvent like alcohol or turpentine), waxes were also sometimes used as or in varnishes.

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- Daub a day ago
  
  True… what I said only applies to canvas paintings. I should have made that clear.
  The longevity of murals is easy to account for: the paint is applied to wet plaster, in that way becoming part of the wall. That is why the murals of Pompeii survived.
  > Canvas is almost always coated with gesso which at the time would use rabbitskin glue as binder, no flax there.
  You are right about the rabbit skin glue, but wrong about the gesso. As I recal, traditional Gesso is a mix of glue plus titanium white powder and is very brittle, generally unsuited to a flexible support such as canvas. A canvas painter would more likely use something flexible like a mix of pigment and rabbit skin glue, or pigment and egg protein or pigment and oil.
  I thank god for modern primers. Using modern primers, I can prime a canvas in two days. An oil based oil primer could take months to dry.
  
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  Mtinie a day ago
  
  As far as I can tell, the ingredients described by Cennini[1] is close to the “traditional” preparation:
  * Gypsum (Hydrated calcium sulfate)
  * Zinc white pigment
  * Clean tap water or distilled water
  * Rabbit skin glue
  —-
  [1] Cennini, Cennino d'Andrea, The Craftsman's Handbook "Il Libro dell Arte," Daniel V. Thompson, Jr., trans. (New York: Dover Publications, 1960) pp. 69–74.
  
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jorgen123 a day ago

> Semi-related anecdote: The first time I went to the Rodin museum I was struck by how badly one of the busts had been lighted. Whilst the guards were not looking, I moved it to a more agreeable position. I came back one year later to find it was still in that position.
That made me think of the old German sketch "das Bild haengt shief" (the picture is askew): https://www.youtube.com/watch?v=a6WQaIIZ248
I hope you left the rest of the exposition standing.

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- Daub 10 hours ago
  
  A very funny video. Thanks. I will keep it as it beautifully demonstrates the waterfall of mistakes that often follow a minor change to a painting's composition.
  Another anecdote: I was once photographing a painting in a museum gallery that did not encourage Phtography. Unfortunately, the light was causing excessive glare. Whilst the guards were not looking, we placed a cigarette package out of view under the frame to lift it away from the glare. Again... upon return many months later the cigarette package was still there.
  I should state that this was a very provisional museum. It had recently been painted, and there were drops of paint of the frames showing that the paintings had not been removed during the painting.
  
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masklinn a day ago

I would assume the mask only covers the damaged areas. This means it replaces manual retouching, so you still need to clean the original painting and remove the varnish in order to get at the original colors, and as part of the usual cleanups (removal of old conservation, stabilisation, infill). The article specifically says that the film is adhered to and via a varnish layer.

Makes me wonder how it would handle heavy impasto tho.

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empiko a day ago

Obviously it can't handle heavy impasto. With heavy impasto, people usually literally sculp the surface using some material to math the rest of the painting and then paint on top of this. Even with minimal impasto, they will often try to mimic the texture by imprinting various tools into the material, mimicking for example brushes used by the original author. This printing method can't do this at all, and the filter might struggle when the painting is too uneven.
Otherwise this might be an interesting technique, if the result can match the color and texture of paint perfectly. I can see it being used for some low priority paintings. There are much more paintinga that need restoration than people with necessary skills, so this could save of them, as it will be more viable to fix them. The infilling is usually just a small part of the entire process, but usually the most difficult wrt how skillful the conservator must be. You must be able to match colors and style perfectly, and there are huge differences in how fast this process is depending on the skills of the painter.

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