I’m currently revisiting a TV show from ages past presented by a lovable old English rogue named Tom Keating, he had a flair for art and began restoring paintings in the 50’s, he subsequently began ‘restoring’ old paintings more comprehensively - beginning with a blank canvas! Being very competent in painting in various styles, notably that of Samuel Palmer he successfully forged a great number throughout the 60’s including Titian, Degas, Gainsborough, Renoir and Rembrandt.
He was caught when after X-rays were carried out on some suspicious paintings he had sold, and revealed some rude words, written in lead white underneath the upper layers of paint in a good amount of them, as well as various other impossibilities in material choices and subject matter he had deliberately added into the paintings.
He used this as evidence that he never intended to deceive anyone as he had clearly left evidence that the works were not original! 
Due to his notoriety, the BBC managed to commission a short series out of him in the 80’s, where he speeds through the processes used in creating his various ‘fakes’ as well as giving a very historically knowledgable run down on the artist in question and their working methods.
I bring this to mind as in the artist round table (9th Jan 2022) I mentioned a peculiar technique of creating an incredibly thin line, by drawing into varnish - which is taken from the following video (watch 14:34 in the YouTube clip at the link below for that bit)
Episode 1 - Tom Keating on Turner
The whole series is available on there too, the episodes are short and well worth a look, as while materials are outdated in many regards, his overviews of the lives of various artists is great. Simultaneously he demonstrates a speedy automacity and fluent technique in drawing which only comes with many hours of pushing paint around.