“This is a Luini painting,” Landrus said. “By looking at the various versions of Leonardo’s students’ works, one can see that Luini paints just like that work you see in the Salvator Mundi.”

He said between 5% and 20% of the painting was by Leonardo, and that Luini was the “primary painter”. [...]

Landrus said: “I can prove that Luini painted most of that painting. A comparison of Luini’s paintings with the Salvator Mundi will be sufficient evidence.”

Describing Luini as one of Leonardo’s two most talented studio assistants (the other was Giovanni Antonio Boltraffio), he has compared Luini’s Christ among the Doctors in the National Gallery with the Salvator Mundi.

The evidence has led him to conclude that Luini was “the only reasonable candidate for much of the authorship”. He added: “By traditional standards, we can call it ‘a Leonardo studio’ painting.”

Landus highlighted stylistic similarities, including the depiction of the gold bands and the fabric on the robes, saying: “One sees a similar construction on both of those gold bands and on the way the drapery is done. Luini did other paintings that had very good gold tracery in them. Also Christ’s face in both paintings has very similar modelling and, while the hairstyles are slightly different, the approaches are quite similar. Also, the shoulders on Christ are very similar.”

Pointing to a photograph of the Salvator Mundi before its extensive restoration, he said: “There’s a lot of missing paint in certain sections. So it really does add to the discussion about how overpainted it is.”

Landus believes that, if Leonardo’s hand is there, it is in the sophistication of the “sfumato technique, the subtle gradations of shading that avoid perceptible contours or dramatic shifts in tonal values”.