There would be no pain, no blood, and no mess.
Or one could take poison.

Of course, there was a certain amount of difficulty in procuring it, but it would not be impossible to find some pretext for buying some laudanum: one could buy several small quantities at different shops until one had sufficient.

Then he remembered that he had read somewhere that vermillion, one of the colours he frequently had to use in his work, was one of the most deadly poisons: and there was some other stuff that photographers used, which was very easy to procure.

Of course, one would have to be very careful about poisons, so as not to select one that would cause a lot of pain.

It would be necessary to find out exactly how the stuff acted before using it.