Martin,

Having just finished a tabletop recently and repairing knots, I would advise
against using any filler in the epoxy. Use the artists oils as one
described and in my case, I used a little gel stain mixed in the epoxy to
match the knots and it worked great. The epoxy did not "shrink" but be sure
to over fill the void slightly since it will slowly settle into the pockets
and you may need to add more after a minute or two.

Clean out the voids the best you can using alcohol, compressed air or vacuum
and either dental pick or tooth picks to get in the crevices to get any
unwanted loose parts out that may not look good in the repair - such as a
broken or partial piece of knot wood.

My experiments of mixing sanding dust (various grits) resulted in very poor
textures that did not match the knot. Epoxy is one of the wood working
glues that is used for it's gap filling properties and strength. I had
about 4 large knots to repair or otherwise secure and several smaller knot
holes that needed filing. I tested several methods on scraps and then on
those defects that were on the back side of the table top first. The
results were always better when no filler was used and it was colored using
a gel stain versus regular (walnut) stain or sanding dust with stain. The
gloss of the epoxy is easily dealt with when you apply your finish top
coats. Just sand the epoxy down and then finish as normal.

I had a knot hole of about 1" diameter and the epoxy fill now looks like a
solid knot. I took a curly (yes I actually do use a hand-plane once in
awhile) and cut it to about 1/4" width and then coiled it and pressed it
into the knothole filled with colored epoxy. The dark epoxy contrasted by a
slightly lighter colored "in lay" of the curly gave it a real knot
appearance. On the other larger knots which were loose, they are now solid
and the epoxy matches perfectly. I also used the epoxy to fill in several
long (thin) cracks that were in the tabletop which I discussed in a recent
post for butterflies (bow-ties).

Practice on scraps, get the color so it matches the surrounding wood and
when filling a knot, ease the epoxy in around the edges. I found using a
small artists pallet knife and single-edge razor blades as great tools for
getting the epoxy where you want it, and then scraping away excess after
it's cured. Let it cure (typically 24+ hours) before you sand / scrape it
down level to the top.

I did use the standard 5 minute, two-part clear epoxy that is found almost
everywhere and it worked fine but I would suggest getting the epoxy that
allows for more open time (15 min) to give you more time to putz around.
Then there's always the West Epoxy System if you want to go with the good
stuff.

Bob S.