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Is it something I'm doing, or is everyone experiencing this.....?

Odie

Odie

Panning for Montana gold, with Betsy, the mule!
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Much of the time, the interior of my bowls have just a little bit less luster after the finish and buff is applied......than the exterior. The sanding is the same......but obviously the grain orientation is different. Could that be the reason why?

discuss.....

ko
 
Just my experience... I find that I need to sand longer with each grit on the interior of bowls to achieve the same finish. I swear that each grit takes longer to sand on the interior. It doesn't make sense, and at times it doesn't feel fair! I should note that I gave up buffing most bowls about a year ago.

It makes me grumpy, but until I have an answer and a work-around, I just spend longer sanding the inside.

I talked with David Ellsworth about this, and he just smiled, laughed, and said, "Maybe that's why I turn hollow forms!"
 
I haven't noticed this, but I'll increase my awareness to see what happens here. Some questions I have are what kind(s) of finish, what shapes (calabash, deep bowl, shallow bowl),is it uniformly over the interior or in certain spots (end grain, side grain), how are you sanding (by hand on lathe, by hand off lathe, power sand on lathe, power sand off lathe), does sandpaper brand matter, how much sanding, how much pressure ..... just trying to think of anything that could have an effect on the final results.

Leo does have a point that light reflecting off an exterior convex surface will be different than light reflecting off an interior concave surface.

Everything we see is like looking into a mirror. By that, I mean the colors of the surroundings alter the color of the object and vice versa. And, the shinier the object the greater this effect becomes. A dull object is like a fogged mirror.... the light is more scattered, but the surroundings still influence how an object looks.

Here's an example of a shiny bowl. Even though the background paper is graduated light to dark gray, notice that the shadow near the base reflects the color of the wood. Since the background paper is neutral gray it doesn't alter the color of the wood, but it does alter its brightness. The lower right is almost as light as the light foreground. The interior is a bit like a parabolic mirror. Notice that we can "see" the umbrella that I used in my lighting. The left side of the interior is looking towards the light so it is much brighter than the right side which is seeing the dark side of the room.

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Zach LaPerriere said:
Just my experience... I find that I need to sand longer with each grit on the interior of bowls to achieve the same finish. I swear that each grit takes longer to sand on the interior. It doesn't make sense, and at times it doesn't feel fair! I should note that I gave up buffing most bowls about a year ago.

It makes me grumpy, but until I have an answer and a work-around, I just spend longer sanding the inside.

I talked with David Ellsworth about this, and he just smiled, laughed, and said, "Maybe that's why I turn hollow forms!"
Click to expand...

One thing for sure, Zach........is I generally start sanding bowl interiors at coarser grits than I ever can with the exteriors.....usually by several grits. The reason for this is tool access. It's much easier for me to get a finer final tool finish on the exterior than it is on the interior......and, this could be a part of the reason the two surfaces, often times, appear to have differing shades of "luster". I quite often am using nothing but hand held sandpaper for all of the sanding on the exterior, but require initial disc sanding on the interior, prior to taking it to my usual hand sanded to 600gt.

Bill adds more dimension to the question.....and the answer. To answer some of his questions......

Watco Danish oil natural, is my usual go-to for a finish, followed by Beale 3-step buff. Most all sanding is done on the lathe, with an occasional piece that has some final sanding off the lathe. I don't always notice a difference in luster between the interior and exterior.....maybe some species are more prone to this phenomena than others.....?......and, it may be purely something I am doing that causes this. In any case, the difference in luster isn't a huge difference. I notice it, but I doubt those people who have my bowls notice it. I'd say the calabash deep bowls are more prone to this difference in luster, than shallow, or platter shaped bowls.

Leo's explanation that the light reflects differently is a likely contributor to this visual effect.

As I mentioned to Zach......I usually use disc sanding on the interior. This is because the tool surface is usually much less refined on the interior, than it is on the exterior. It also includes more tear-out than I ever get on the exterior......and, I know that is a contributing factor to how well a finish will take.....if the disrupted fibers go deep enough. That could be a part of this equation, as well. I'd say average wise.......I start sanding at around 100gt on the interior......but, my average start sanding on the exterior is at 240gt......that, in itself, is a pretty big difference.

ko
 
Ditto what Nicholas said. I photographed artwork for 26 years. What is happening is you have to imagine the inside is like a mirror. when you look at the an area near the rim you are looking down and what you would see if it was a mirror is the reflection of the inside which of course is wood. This is usually darker that what a mirror on the outside would see which is the the background paper of brighter things in the room. On rare occasions I have put white paper or aluminum foil on the inside of bowls just out of camera view so that it is reflected in the interior wall and makes it brighter.
 
I was thinking form and light were the culprits as well. For sure, the inside of a bowl is more difficult to turn than the outside. Part visibility, and part tool access, though with the sliding headstock, that is not a problem. Maybe another consideration here is I tend to hold my tools level and roll them over for a higher shear angle rather than the more common 'drop the handle' for the high shear angle, which is difficult to impossible on the inside, especially on a long bed lathe. I do start at the same grits inside and out. I shear scrape the wall, and transition, and am now using a NRS for the bottom and some times the transition. This removes all of the 'ripples', which is where most of the sanding is needed, and tear out is minimal. More experimenting with the NRS...

robo hippy
 
Leo Van Der Loo said:
scattering of the light in the interior of the bowl,
Click to expand...

I'd bet on that

odie said:
is I generally start sanding bowl interiors at coarser grits t
Click to expand...

I'd bet on Leo's notion because I rather suspect you are neither skipping grits or leaving coarse grit marks.

But as you prolly know all too well the center of the vessel doesn't have the same surface speed across the grit as the periphery and maybe just maybe that factors in.
 
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