Thread: Wood Chatoyance

Thanks Neil

I've been discussing with some people about this drop in chatoyance during the progressive grit sanding test, and we came to this conclusion: it was due to the fact that the 320-grit disc we used was a partly worn one, thus giving an even smoother surface than the 600-grit disc (which was new). So I believe that, in general, a higher grit always yields a higher chatoyance, and a worn disc corresponds to a higher grit new disc.
However, some more tests of this kind are planned.

Take a look at this set of tests:
Surface preparation on Curly Maple – PZC Chatometry
We showed that (at least on curly maple finished with BLO or shellac) sanding to a higher grit provides better chatoyance on the finished product. No sanding at all gives even better results (at least on this curly maple veneer).
We plan to check if the common knowledge "a good planing is better than any sanding" is true.

This timber was purchased dressed 40 years ago and kept under our house for 30 of them before being turned into a mantlepiece.

Cheers,
Yvan

PS Apologies for the pic's orientation...most irritating!

Originally Posted by chatometry

...we came to this conclusion: it was due to the fact that the 320-grit disc we used was a partly worn one, thus giving an even smoother surface than the 600-grit disc (which was new). So I believe that, in general, a higher grit always yields a higher chatoyance, and a worn disc corresponds to a higher grit new disc.
However, some more tests of this kind are planned. ....

Perhaps it has more to do with a worn sandpaper disc burnishing the surface rather than sanding. The worn grits will sand to some extent however the filled pores between the grits or the matrix will burnish the surface.

Thank you for sharing this very interesting research.

Originally Posted by yvan

This timber was purchased dressed 40 years ago and kept under our house for 30 of them before being turned into a mantlepiece.

Cheers,
Yvan

PS Apologies for the pic's orientation...most irritating!

If it changes in appearance (colour, tone, optical movement) as you walk past it then that is chatoyance. If it remains static I would just call it figure.

Nice bit of wood, either way!

Originally Posted by chatometry

Take a look at this set of tests:
Surface preparation on Curly Maple – PZC Chatometry
We showed that (at least on curly maple finished with BLO or shellac) sanding to a higher grit provides better chatoyance on the finished product. No sanding at all gives even better results (at least on this curly maple veneer).

We plan to check if the common knowledge "a good planing is better than any sanding" is true.

Traditional Japanese carpenters definitely favour a sharp finely tuned plane finish as do many western wood workers.

A point of clarification... were any interim grits used in that Curly Maple test between #240 and #1500, as you did in the 'Progressive grit sanding' test?

Your 'Progressive grit sanding' test results were very instructive, but that was without adding a finish at any grit point. If you did use interim grits between #240 and #1500 in your Curly Maple surface preparation test that helps to partly answer a question about adding a finish to pieces that are sanded above #240.

Originally Posted by yvan

This timber was purchased dressed 40 years ago and kept under our house for 30 of them before being turned into a mantlepiece.

Cheers,
Yvan

PS Apologies for the pic's orientation...most irritating!

Nice piece! Do you know what wood it is?

Originally Posted by NeilS

Traditional Japanese carpenters definitely favour a sharp finely tuned plane finish as do many western wood workers.

A point of clarification... were any interim grits used in that Curly Maple test between #240 and #1500, as you did in the 'Progressive grit sanding' test?

Your 'Progressive grit sanding' test results were very instructive, but that was without adding a finish at any grit point. If you did use interim grits between #240 and #1500 in your Curly Maple surface preparation test that helps to partly answer a question about adding a finish to pieces that are sanded above #240.

Yes, interim grits were used to reach the final 1500-grit.
However, no interim finish was applied.

I know that a better technique involves sanding, then finishing, then finer sanding, and so on. This could be an objective for the next test.
Would you suggest a specific recipe?
Proposal:
Sanding to 240
Medium shellac
Sanding to 400
Medium shellac
Sanding to 1500
Dense shellac (as many coats as required to achieve chatoyance stabilization)
?

Thanks
Paolo

Originally Posted by chatometry

Nice piece! Do you know what wood it is?

Oops, I should have mentioned it: myrtle

Originally Posted by chatometry

Proposal:
Sanding to 240
Medium shellac
Sanding to 400
Medium shellac
Sanding to 1500
Dense shellac (as many coats as required to achieve chatoyance stabilization)
?

Yes, Paolo, that would fill in the missing data point between #240 and #1500.

The practical benefit of that is that most craft woodturners go higher than #240 and few go as high as #1500. Somewhere between #360 and #600 is where most turners stop, but if there is a proven benefit of going higher with a particularly chatoyanced piece of wood then some of us might add the additional higher grits to our sanding procedure.

Thanks Neil
I will run this test.

Paolo

Happy to send you some samples of Acacia Celsa
I took this pic in torchlight to try and capture any chatoyance
The grain has 'lit up'
Log Dog

Originally Posted by Log Dog

Happy to send you some samples of Acacia Celsa
I took this pic in torchlight to try and capture any chatoyance
The grain has 'lit up'
Log Dog

Amazing. Acacia seems to be the most promising genus, and those species that yield brownish wood should be the best. However, it might be worth trying to dye one of the lighter ones and see what happens...

Originally Posted by NeilS

Yes, Paolo, that would fill in the missing data point between #240 and #1500.

The practical benefit of that is that most craft woodturners go higher than #240 and few go as high as #1500. Somewhere between #360 and #600 is where most turners stop, but if there is a proven benefit of going higher with a particularly chatoyanced piece of wood then some of us might add the additional higher grits to our sanding procedure.

...eventually, test done!
The results are shown here:

Incremental grit and finishing on Curly Maple – PZC Chatometry

It appears that sanding to a higher grit generally provides better results, although going above #800 is not always useful.

Honestly, this is just one test campaign on one wood species with just one finish, plus it was made on veneer, so I cannot really generalize the results to other wood species with other finishes in solid form. Still, in such a complex world, I would sand my crafts to a high grit either before or during finishing, at least where easy (flat surfaces and turned surfaces).

I hope this helps, and any suggestions for further testing are welcome.

Paolo

Originally Posted by chatometry

...eventually, test done!
The results are shown here:

Incremental grit and finishing on Curly Maple – PZC Chatometry

It appears that sanding to a higher grit generally provides better results, although going above #800 is not always useful.

...

I hope this helps, and any suggestions for further testing are welcome.

Paolo

Yes, very useful Paolo.

Many thanks