Why would you think this is a forgery?
It has all the elements of a classic forgery process. First, get a historically correct frame so the history is legitimate by dating. This is fairly easy to do because the art in of itself is not devalued if you put brand new framing on a historical or any painting. The frame is merely the vessel to what is valuable. Kind of like a Porsche 911 is a 911 regardless if stored in a luxury condo garage with 24/7 security or parked in the ghetto. So you can toss out the frame for relevancy.
The next part is to look at the image. Another stage in forgery is to copy elements of well-known paintings of the artist and copy those elements, yet add new elements to look authentic. In this case we can see the near identical nose, lips, eyebrows of Mona and Jesus as well as even the hair treatment. The dress of the Jesus is fairly similar with translucent layering and the fine embroidering. The difference really is in the background. In this case a solid black background vs. an intricate kind of fantasyland background of the Mona Lisa. If you were going to copy, the easiest solution for variation is the black background common in other medieval artists. But did Leonardo use black backgrounds in his other paintings? Let's take a look.
In this case, we find that Leonardo did use a dark, but not solid black background. So the fingers look like a good match, yet the background doesn't appear to be what Leonardo preferred. So either it was painted this way as a one-off or maybe filled in afterwards. Returning to the eyes, you can see that Leonardo always paints the figure looking at the viewer while the Jesus Christ figure is kind of looking cross-eyed. So the eyes execution is fairly poor. Now if this were merely doing a local priest or nobleman, then maybe the eyes would look this way. Or did the painter just not have the talent to copy the eyes well?
Another tell tale sign is the shoulders of the Christ figure are short. If you compare to John the Baptist, the right shoulder to neck is about twice the Jesus figure. Did he paint Jesus cross-eyed and with incorrect shoulder length? You have to remember that Leonardo was considered to be of High Renaissance period where perfection in the body proportion reigned supreme.
If we look at the expression of the mouth, we see that in both John the Baptist and Mona Lisa, both figures have a mischievous look of either hidden glee or unknown thoughts. Looking at the Jesus figure the expression is kind of dead on arrival look or stoned off his ass. This would suggest another painter did the Jesus figure that just could not master the excellent hidden expression of Leonardo's figure.
This drawing of Leonardo da Vinci proves he intimately understood the proper proportions of the human body. Even this generic man is shown as scowling being shown naked vs. the dead pan Jesus figure. You can see in his self portrait the look of deep pensive thought while Jesus has no thought. Would he really of portrayed Jesus as dead emotionally? You have to remember this period.
Here we have Caravaggio that did paint in all black, but decades later after Leonardo. He portrays himself here as Goliath slain by David. Now why am I showing you this? The Pope had put a death threat on Caravaggio that forced him to be constantly on the move. Now if you can paint like this and still have the death penalty, would Leonardo have painted the Jesus with dead pan eyes and risk his own death warrant by Rome, his biggest patron?
Have there been other famous forgeries in the techniques you suggest?
Yves Chaudron supposedly stole the Mona Lisa and made 6 copies of it in 1911. He then sold via a dealer Valfierno in France and up to 6 copies to the United States. However none of the six forgeries ever came to light. Of course, how could they come to light as everyone knows the Mona Lisa and the copies would just be seized and possibly destroyed by the authorities. None of the art of Chaudron came to light speculating that he was in fact made up by an author and perpetuated.
Another famous forger was Han van Meegeren. He copied Vermeer paintings by buying old frames to date the painting correctly. He would paint mixing raw pigments into linseed oil and bakelite. Then he would bake the paintings slowly to get the correct crackeling effect to show the "age" of the painting. He managed to sell even to high-end Nazis like Goering fake Vermeers that Goering swore were original. After the war, people thought he was an art dealer selling off Jewish paintings to the Nazis, so he confessed to being a forger to not get hung as a war criminal.
But hasn't the new Leonardo been certified for six years?
Yes, this is correct, but keep in mind the verifiers. The verifiers don't want to be fooled, but at the same time would love to have the reputation enhancement of "finding" a new Leonardo. The incentive for the auction house is obviously $50 million in commission for the real deal vs. zero for a fake. It has been proven that 100s of works have been sold by Christies, Sotheby's or other high end auction houses that were fakes. In Jan 2017, "St. Jerome" was said to be fake sold by Sotheby's for $842,000. In October 2016, "An Unknown Man" portrait fake was sold by Soethby's for 8.4 million euros. The list goes on and on.
Are they other artists copied?
Above we see Jackson Pollock, whose style seems easy to copy with drip painting. Any artist with an easy to duplicate style is a prime example of forgery. Miro comes to mind.
Why do so many of the fakes land up at the big auction houses? Don't they offer a refund of some sort?
They do offer a refund. Did you know it usually is only up to 30 days? So basically the gentleman or lady that paid $500 million on the "Leonardo" only has a small window to prove the authenticity of a work and ask for a refund. How ethical is the artwork you spend millions on, only to be told its fake 2-3 months later and then not be able to regain your money? Another thing is in 2000, both Christie's and Sotheby's were accused of price collusion to keep prices high on sold artwork to keep a larger piece of the buyer's commission from the buyer. Does it sound like they are protecting the buyer?
Is there a worse offering than an auction house for risk of fakes?
In fact there is. My ex-boss of multiple galleries told me of the fakes sold on cruise ships. In 2008, Park West, which sells about $400 million each year on cruise ships, was accused of selling forged Miro prints on board by 11 defendants. Despite the scandal, Park West continued to sell on Norwegian Cruise lines as well. The only change was now they offer 40 day refund period. So if you check within 1.5 months after a cruise, you may get your money back. If you happen to board one of these cruises and try to warn guests, you are booted off the ship. How is this legal? How is it $400 million legal? Additionally, the cruise ships usually call the Isle of Malta as their home port, so to sue them you have to go to the International Court of Human Rights they do have there and they don't hear criminal hearings. In essence, the boats are completely safe from prosecution. During some of the scandals, they auctioneers had the printing press right aboard the boat to print off the fakes on demand. As all auctions state in bold lettering...
ALL SALES ARE FINAL
Do you have a painting about fakes?
This painting is about politics of the moment. Trump as president called out CNN as fake news on live TV and refused to let them respond as traditionally happens. In essence, he knee-capped them publicly. TV news journalists responded by posting all the journalists that died covering the "fake news" of the Iraq and Afghanistan wars on Twitter, DT's favorite mass medium to circumvent national TV news. The fake part is that it is copied from a photo and the logos from the real logos.