Two tone on bottom of bowls

[Hugh]

I have a question for all of you. I turn most of my bowls out of green wood. Mostly hollow vessels. I start with a chunk of wet wood and turn a tennon for the chuck to grab. I usually leave a little more wood than that for me to finish up the bottom of the vessel. When I finish turning the outside, I hollow the vessel out. Usually down to 3/16" or so. Then I take the 90% finished vessel out of the chuck to reverse turn the bottom. When I cut away the tennon and what ever wood I have left on the bottom I end up with a lighter colored ring on the bottom of the vessel. The two tone color stays there even after the vessel is dried. The two tone stays even after I have sanded the dried vessel. Anybody have a solution to this?????????
Hugh

 

[C Edward Moore]

Burnishing?

Hugh,

Here is a POSSIBLE explanation, but it may not apply to your turning methods. Some people use a tool like a spindle gouge to remove the tenon and to clean up nearby. When using this tool they rub the bevel with sufficient force to almost burnish the wood. If you think of this with the orientation of the bowl determined by looking at the bowl from the top, then the bowl is turned with a counter-clockwise orientation. But, when the bowl is reverse-turned, the bowl is now turned in a clockwise direction. So, on the outside of the bowl the upper portion is turned in one direction and the lower portion is turned in the opposite direction. Think of this as laying the fibers over, not unlike on a carpet. This will make one area look darker than the other.

Sanding will smooth the surface, but unless you use an aggressive grit, it won't undo any burnishing that occurs.

This explanation is particularly evident when removing the tenon from the bottom of an end-grain box. Burnishing with a spindle gouge heel can leave rings on the bottom that don't want to go away.

 

[J. Fred Muggs]

I agree with Ed. Even if you're not burnishing, any fibers left would be "bent" in opposite directions. This would cause the light rays reflecting from the surface to look differently.

 

[MichaelMouse]

Answers seem 180 out.

An area which is burnished/overheated or merely cut cleanly will show as dark. The lighter area would be the one which was scraped by the side of your parting tool, for instance, a common occurance. I would give myself enough space when parting off to complete the final cut down to 3/8" or so with one tool. Ideal is a beading tool or straight chisel, which is more forgiving than a skew point up, where it's easy to tip down faster than cutting in, with dreadful results. I like a 1/4" gouge for the job.

Saw most of the remainder off, and use a curved knife to whittle the last nub. I prefer the knife over a gouge because I can hold the piece with one hand and the knife with the other.

 

[Fred in NC]

Hey Fred !

We must be related. Your pic looks just like me !

 

[dkulze]

Another effect I've gotten sometimes is that, when you use a compression jaw chuck, you do just that, compress the wood. This doesn't just compress where it touches, it can compress a column of wood that reaches into the base. I'll frequently see marks even if I've carved the base. Only way past this I've found is to sand past it.

Dietrich

 

[Hugh]

You have given me food for thought. I like the idea about the bowl being cut in the opposite direction and also the compression of the wood. I have tried to sand this area a bit extra thinking that it would go away. But on some woods it never seems to leave. I do not want to sand too much as I will change the shape of the bottom of the bowl. I have also been trying to make my vessels fairly thin and there is not a large amount of wood there to get rid of (if I am lucky in my turning). I need to think about this some more. I do my best thinking when I am turning - So .....
Thanks gang!
Hugh