Renaissance oil paintings can suffer from degradation of colours over the centuries as candle soot accumulates, and chemicals oxidise.
This can make vibrant colours dull and muddy, for example, green pigments were often made with copper soaked in vinegar to make a copper acetate which is then mixed with boiling linseed oil. Over time cracks in the painting surface let in oxygen and the verdant green grass turns brown. Its even worse for silver which was often made with metallic silver to give a real glint to armour - of course it oxidises to black.
The colour changes are somewhat predictable as we can recognise things like grass, leaves and armour, and we know most of the pigments used. So in theory it should be possible to use darktable to reverse the colour changes and see the painting as the artist intended.
I can’t find anyone online who has tried this, and maybe its even a challenge for darktable.
Does anyone have any thoughts?
As examples in the Uffizi we have Botticelli’s Primavera
I’m pretty sure that there is no copyright in a photograph of a 15 Century artwork, although there may be some issues with a hi resolution digital scan provided by the owning gallery. Certainly all galleries will try to get you to pay some licence whether or not it is legally required, so it may be difficult to get hold of a base image to work with.
I think the chemistry involved is a bit more complicated than just deposits of soot and oxidation. E.g. metallic silver wouldn’t react with oxygen, but rather with sulphur compounds, giving initially a brown tint. Also the linseed oil carrier and varnish can change colour over time. During the oxidation of the linseed oil, radicals are formed that can react with a wide variety of other compounds. And light also plays a role with some pigments.
Added to that, there’s a wide range of possible pigments, of varying stability (and price!), and some techniques use layers of transparent colours (glazes), or mix pigments.
So, given the number of variables, I doubt you can get any reliable colour restoration just from a scan/photo of a painting. You could create an impression of what the original may have looked like when it was newly painted, but I think that’s the best you can hope for.
As for fees to get images, they are perhaps not copyright fees (hard to explain for a 16th century painting), but e.g. if the gallery is a private area, they can ask a fee to allow you access or to allow you to photograph anything.
I think digital restorations do exist real since quite some time - with Photoshop. However I cannot name any literature on this.
But the real restorers are doing quite a good job, too.
I mean a digital restoration is not really optimal - sometimes, when there is no money to do a real restoration, they are better than nothing.
Often, they are also part of a real resturation, as a kind of preparation. Resturations - digital or not - are always an interpretation.
Indeed, restoration of old paintings is done since a long time. But afaik, most use quite a bit more information than just a colour picture of the artwork in its unrestored state. Things like chemical analysis of the different paint layers, X-ray, infrared and UV imagery, etc.
So, getting the picture back in the state “the artist intended” using darktable on a photograph or scan of the picture is, IMHO, impossible.
What you mean is called technical art history. It’s a really interesting topic. But there are lots of questions that even technical examinations cannot answer… in my opinion, in most cases, with a bit experience, it is indeed possible to imagine what the painting looked like when it was new. I mean it’s usually the varnish that gets yellowish, then there is also the krepiertes Blau etc.
In many cases, technical examinations only prove what art historians suspected. And they are so expensive! I would not overestimate the power of technical art history. I mean I am a real fan a technical art history, actually it is maybe even one of my research areas.
We have a lot of experience with real restorations. We know meanwhile quite well how a painting looks if the varnish is removed and/or renewed. So one can draw many conclusions from that.
But in the end, everything is interpretation.
I guess its not so easy, otherwise it would have been done already. Having said that, I did pump up the green leaves to the max in the Botticelli, plus more blue for the Sky and Winter coming in from the right side and it is interesting . …
For example, we can attempt to detect and remove craquelure from Mona Lisa’s left eye.
To do this, I had to made assumptions about which marks are caused by craquelure. This was fairly easy for the dark marks, and not so easy for the light marks.
I don’t have anywhere near enough technical knowledge of pigments and how they age to attempt a “colours as originally painted” version. But we can have fun trying:
There are some excellent youtube videos of actual restorations/repairs of artworks. Something that i had always wondered about how it was done to a physical painting. Just removing the old varnish was a major step as it revealed the hairs of the people. they were a dirty smudge before. Digital will present it own challenges, that may not produce the full detail an actual restoration would.
digital “preparations” of a physical restoration are mostly used when parts of a painting are missing and those need to be completed - first they try (simulate) in Photoshop what looks best. Because that’s actually an artistic decision.
I know this is an old topic but I’m looking for some guidance. I have a 10 year old acrylic painting that I made as a gift for my twin brother’s wedding but I didn’t varnish it/know how to preserve it properly as I was new to painting (and probably also over diluted the paints, or added too many layers etc). I want to see if I can restore it digitally for a print for his anniversary. Do you know any apps or services that I could use now that AI is even more prevalent now I feel like this should be a thing. The free apps/tools online are still pretty bad however…
We should always start with a high quality image, not a JPEG.
Here is an attempt to make the white lines transparent, and then Filling holes in priority order (“inpaint”). The priority order preserves edges that are continued into the holes. Windows BAT script:
