Those double black lines on your violin are not drawn in decorations. They come from this:
That purfling strip gets bent with an iron and stuffed into a channel, which we cut out with knives and pick out with this:
And in the process, we smash our left thumbs with the hard tempered metal of the purfling pick.
We knife two lines, 2mm deep, but there’s no real way of knowing how deep we’ve cut other than guessing by eyeballing how far down the tip of your knife has gone. Also, keeping that channel perpendicular to the surface is no easy task!
So when picking out the channel, you sometimes come across a spot where your knife didn’t reach, and the channel is unclean.
But wait… that looks familiar.
Okay here is the update on violin #1:
maple back with purfling all glued in: