Some of the prettiest woods have inherent cracks, voids, and open pores. Examples are Honduras Rosewood burl, Ebony, Desert ironwood burl and Ringed Gidgee. Burls, fossil ivories, and bones also have these issues. Some woods when stabilized develop cracks. There is no need to toss these potential handle materials in the firewood box or trash bin. Most of these issues can be filled and either made as a feature or made to virtually disappear.
Occasionally cracks will develop due to peening a pin or with age. This does not necessarily mean a ruined knife.
Cyanoacrylic resins, also called Super glue or Krazy glue come in a variety of hardening speeds as well as viscosities. They also come in formulae that needs an accelerator spray to make them harden. The minimum “kit” for working wood is a bottle of clear resin in thin, medium, thick, and black. Black is useful for filling voids to look like knots as well as applying a contrast in certain woods.
Places like Amazon and Woodcraft sell many varieties used by woodworkers. My favorite is from Knife and Gun finishing supplies, which also does all of my wood stabilizing. Their thin CA glue as well as their accelerator are well priced and high quality.
NOTE - Buy the accelerator/activator from the company that makes the CA you choose because they are not all the same.
About CA Glue: Cyanoacrylic glue is a resin that is catalyzed by water molecules in the air, or in the materials being bonded, into an acrylic resin. This is why skin instantly bonds if you accidentally get it on your fingers. The catalyzation can be sped up by a spray of accelerator/activator if needed. The enemy of storing CA glue is temperature and humidity. Keep bottles tightly capped and store in a cool place. Buy in bottles the size of your normal use for about 6 months. A quick wipe of the spout with a clean paper towel before putting the cap back on will keep the cap from getting clogged with glue. The thin resin sets fastest, medium and thick are slower. Each has its place. Cheap CA glue is usually low quality and diluted. Get a name brand that is made for woodworking (see suggestions above). I’ll dispel a myth that you may find online - there is no cyanide in CA glue. However, the vapors can make your eyes burn and may cause breathing difficulties if you have asthma. Work in a well ventilated dry area. The chemical reaction is exothermic, and gives off heat. If you use the accelerator on a large amount of CA it may give off some “smoke”. This is just vapors of water and the solvents. Large CA joints or fills may get somewhat hot, but this is usually not a problem.
The trick for any good handle finish is this – The finish should be IN the wood, not ON the wood. This is how a CA finish works. When done all you should see is smooth wood.
A second thing to learn is you need to let all resins and glues fully cure for at least a day … and up to a week in some cases … before final sanding and polishing/buffing.
Set-up
I repeat - work in a well ventilated dry place where smells, glue drips, and dust won’t be a problem. Wear rubber gloves and old clothes. Have a roll of paper towels at hand. Tear off a few dozen sheets to have ready when needed. I often tear these sheets into 1/4ths.
Have acetone on hand to clean up drips and for when (not if) you get it on your fingers. You will also need the acetone for applying the CA finish. Some folks use nail polish remover for applying a CA finish. That is fine, but I use plain hardware store acetone purchased in gallon cans.
Put down cardboard and newspaper to catch drips. A shallow plastic storage bin with a few sheets of newspaper in the bottom makes a great work station for CA work. Keep your CA glue in an airtight plastic box when not in use. Find one the right size to keep the bottles upright. DON’T store the accelerator with the CA glue.
Tear plenty of 120 and 220 grit sandpaper into small squares. About 3”X4” (1/8 sheets) is a good size. Place them in separate storage boxes or zip-lock bags. You can’t easily detect which is which otherwise. Cheap AO paper works fine here, as you are only sanding the handle to seal it. Once the handle is sealed and filled, use your normal finishing papers and procedures.
Procedure
While the following works for most any wood or material. Stabilized wood is by far the best choice for many reasons. It takes a much better final finish, too.
The trick in filling most small pores and cracks is to fill them with the wood. Properly sealing the grain and filling the pores also makes for a higher polish in the final sanding and buffing. Start by sanding and shaping the handle to around 95% done. You need a little extra to be removed in the sealing and filing steps. It should be at a 120 grit finish at this point. The handle should be clean and dry.
For open grain and porous woods – All you need to do for these type woods is fill the pores and grain. Almost any wood will benefit from this procedure. It works very well with woods you might not think need it, like ebony and walnut.
Flood the handle with thin CA and let set for a few minutes. Sand the surface with 120 grit paper until smooth and all excess CA is sanded off. It may still be uncured, so make sure you are wearing rubber gloves. It will also gum up the sandpaper, so have lots of 1/8 sheets ready.
Next, flood again with thin CA and let sit until tacky. Sand a bit and then wipe with a paper towel wet with acetone. The acetone will dissolve the surface acrylic resin. Immediately continue sanding. This will make a mix of gummy CA and wood dust that works into the pores. Wipe off with a dry paper towel as you sand to remove any sticky dust, then wipe with the wet paper towel again to dissolve more of the CA. You want the paper towel damp, but not soaked, with acetone as you sand. Reapply the CA again as many times as needed to fill open pores and grain. You will know when it is all sealed because the sanding will get easy and leave a very smooth surface. Stop using the acetone wipes as the surface shows all wood. Clean up with 220 grit paper and check for a complete sealing. Finish the handle by sanding up the grits to at least 1000 grit and then buffing. It should have a lovely shine. If you find dull spots it is either because you have CA on the surface that has not been sanded away, or a spot that is not fully sealed. If it is a spot that is not sealed. Repeat the CA and acetone in that area again until sealed. Some folks, like Bruce Bump, apply a CA finish with as many as ten flood/wipe/sand repeats to get a glass like shine on their wood handles. Old mammoth ivory can be sealed and made much more stable with this flood and sand procedure.
For wood with small voids and cracks – These woods need a bit more than simple sealing to become show stoppers. However, they often are the prettiest handles. You need to plug the voids with resin and wood dust before starting on the final finish.
Start with flooding the handle and sanding all the CA off as with the open grain wood. Just two flood and sanding steps is all for now.
Look at the voids and decide which can be filled with the CA/wood dust slurry and which will need more filling. The larger voids and cracks can be filled with black or brown CA and sanded to add wood dust to give a knot effect or other unique feature. Clear works well on smaller voids and will make a fill that matches the wood color. You want a medium or a thick CA for these tasks. Work on one side at a time so it does not drip all over the place, or in some cases, a small area at a time. Fill the voids with the resin and let it soak in a bit. Add more until it stops absorbing, then give it a shot of accelerator. NOTE – pay attention to where your CA bottles are when spraying the accelerator. The bottles should be well away from the spray path.
Apply a few drops more of CA if needed and let it set up for several minutes and then sand with 120 grit (no acetone wipe).
Once all voids and cracks are filled, start the flood and sand with thin CA to fill the grain using120 and 220 grit sandpaper and acetone as above. As before, you want to make a slurry of wood dust and CA to plug all the tiny voids and grain. Use a paper towel wet with acetone to keep the CA semi-cured as before. As the surface gets closer to fully sealed and smooth, back off the acetone and sand to a smooth surface. Then finish up the grits and buff. Be more gentle buffing wood with voids to prevent melting or smearing the acrylic filled spots.
For wood and fossil material with larger voids and cracks - These materials need serious filling to make usable. Sometimes a section of mammoth tusk will be partially delaminated, or a piece of burl wood will have larger voids. These are salvageable by filling the voids. This has recently become popular with the use of acrylic casting resins dyed to any color you like. Many handle suppliers sell scales or blocks made this way. The block or object needs to be contained in some sort of way so the resin can fill the void while curing. Casting suppliers sell silicone molds the hold many size object and are reusable. Other things that work are small cups or cut up drink bottles. I have taped up a mammoth tusk section with electrical tape and left only one end open. I taped the open end up past the lip to allow a reservoir of resin as I poured. For ivory, black makes a great contrast color. The resins for these tasks are available everywhere as well as Amazon. It is a two-part resin and must be carefully mixed … preferably by weight. While the acrylic resins will work, it is far better to use the epoxy casting resins for our purposes. They sell dyes in any color you want to tint them. Other things like mica powders and fillers can be added to create interesting effects like sparkles or make the filling opaque.
Once the voids are filled, the wood can be sealed and sanded as above. Once the voids are filled use these materials as you would a solid block, being careful not to get it hot in sanding and buffing.