Not the commonest knotting on the market, to be fair.
I use clear knotting sometimes when I do carved lettering.
I paint Liberon's version in the finished cut to seal the edges and to prevent colour bleed creeping along the grain and discolouring the surrounding wood if the lettering is to be painted.
Clear, or more accurately, very light knotting, has been around for a while...... though some makers' products are 'clearer' than others.