Replies

1. 
   JerryW | May 21, 2010 10:01pm | #1

   You asked two questions - how to fill small gaps around dovetails and how to finish walnut to conceal sapwood.  To get some insight into the gap filling issue, look in the current joinery post listing (http://forums.finewoodworking.com/fine-woodworking-knots/joinery/help-filling-small-dovetail-spaces) .  There is a lively discussion and lots of answers.

   Relative to finishing, I have worked with walnut a long time and generally finish it naturally without staining.  I like the natural color and the fact that it is a wood that has a substantial amount of "irredescence" which sort of allows you to see into the wood.   I tend to avoid sapwood by not selecting it at the source, however my approach on sapwood would be to try to blend it in by using a light walnut colored, oil based stain (such as minwax or General Finishes) on only the sapwood and rub it it off until it matches.  Try it on some scrap, allow the stain to dry for at least 24 hours (despite what the can says!) and then apply a clear topcoat and see how it looks.   

   Good luck - lots of folks use a lot of sapwood in walnut projects due to cost considerations.  It can be quite attractive and act as highlights in such things as book matched panels.

   Jerry

2. 
   SteveSchoene | May 21, 2010 10:10pm | #2

   Walnut sapwood

   is best left in the scrap bin, unless you are working it into the design of the piece. 

   That said it is possible to match sapwood to heartwood, mostly through the use of dye (I recomment powdered watersoluble dye, even though it is slower than alcohol solvent dye)  applied selectively to the sapwood.  You have to select a color that matches the heartwood when it has been wetted with finish--you can simulate this by wetting with mineral spirits.  Apply the dye to the sapwood with a rag and then use the water on a rag to feather the edge between sap.and heartwood.  Then seal the dye with a single coat of shellac, though if you omit this step the pore filler will act as a stain, coloring more than just the pores.   You can also apply a oil based stain over the dye to color the full surface.,  Then use a slightly darker shade for the pore filler to add depth  to the finish..   

   You may like the richness of color that you get if you first do an overall dye coat of an amber or orange dye (not too strong), and then match the sapwood to the heartwood. 

    For a film finish look, a pore filler is recommended.  I like to tint it just a bit darker than the background color of the walnut.  Oil based pore fillers work best.  You might look for Old Masters pore filler which contains a high proportion of silican which gives a filler that shrinks little.  You can tint using universal pigments, japan colors, or artists oil paint.  After the pores have been filled and the filler given ample time to cure--increase the time given on hte label to be safe, particularly if the temperature in your finishing space is consistently under 78°

   You can then use the top coat of your choice.  Shellac looks nice, or you can use an oil based varnish, optimally a non-polyurethane varnish. 

   OOPS.  I just noticed you intend stringing.  Are you sure>  That seriously complicates matters since most stains and dyes will color the string at the same time as the walnut.  That suggests a chemical stain that doesn't color the stringing but does darken the walnut.  Potassium dichromate could work, but I hesitate to recommend it since it is poisonous and a carcinogin.  You may want to reconsider trying to have a very dark walnut finish.