Whenever you burn on pine "make sure pine is thoroughly dry....fresh cut the sap will tend to 'spark' ... also don't burn on any chemically treated pine . Submitted by Barb Cramer

The following is a response to a forum question about burning on pine and contains more insight from Barb:

A lot of my burnings are done on pine...really a challenge working
with it. When you switch to one of the Poplars or Birch species of
wood you'll find you get much better results.

Anyway to answer your question ... did you SAND the wood REALLY,
REALLY good? It is important to sand to a satin finish as much as
possible. Also, you may be applying too much pressure ... no need
to press hard, let the pen do the work...you may have to go over the
lines a couple of times.

A trick I use - when the grain of the wood is causing problems I
sometimes "slice" through the raised grain areas with a utility
knife before burning ... use of an Xacto to go over the pattern
lines creates a bit of a groove & minimizes the bumps somewhat.

You might try using the finer or sharper edged "Universal Point" tip
when doing the first burn over your pattern lines.

More helpful hints from Cheryl:

When I go across a real tight grain, rather than
pull the tip toward me, I push it away from me, I find this gives me more
control and allows me to make a more even burn despite the bumpy grain.
Also, I found that going over the burn several times to darken it as much as
possible helps eliminate the bumpiness from the grain. Unfortunately, it
makes for more of a monochromatic burn. Lastly, but most importantly,
choosing a pattern that follows the contours of the grain line always makes
burning easier, especially when burning pine.