Many times a fine piece of well figured waddle walnut will have a badly checked knot. File the check out until you have about 1/8″ vertical surface all the way around. Then plane a scrap of similar and colour to 1/8″ thickness and tape it over the opening so that the grain closely matches the solid stock. Turn the entire unit over and spray a coat of latex paint through the back to give the exact shape of the check, then cut, file and sand the plug to give the exact fit. After gluing in and filing from the back for support and sanding, it will be hard to spot this easy repair job.
Latex paint is a misnomer because there is actually NO latex in latex paint. Latex is a natural product that originally came from the Brazilian rubber tree (Hevea Brasiliensis) and is now mostly produced in SE Asia. The sap of the Hevea is the natural product from which real rubber is made and this is what is used to make latex gloves; it is also the product to which people are developing allergies. This natural latex product is not the same ingredient that goes into paint. What goes into paint are synthetic polymers that look just like natural latex but have a completely different chemical makeup and different properties than latex rubber.
So if a customer announces that they have an allergy to latex, you can answer with confidence that there is none of THAT kind of latex in your paint.
Our brothers and sisters in the UK use the general term “emulsion” instead of latex but it is the same type of paint that the term “latex” paint is used in the United States.
Another method would be to use epoxy and die mixed and thin epoxy would be a better option so it can sink into and fill the check. Let it dry over night and plane the surface. This won’t mask the knot but it will fill the checks and solidify the knot.