'Dichroism'; in the ground or 'varnish'?

[John Harte]

Peter K-G, thanks for showing what I dismally failed in an earlier post. This is another try, moving the light and camera and using a neon-like tube bulb. It could be just light reflectance as Don suggested, but isn't light shift the alternate of the surface moving to create the change. I did put on another coat.

 

I think top wood is the challenge and I wish this is also shown in posts.

 

Fred, are your photos taken under a single light source?

 

If there is any other light present in addition to your neon-like tube bulb, you may be getting colour effects due to the interaction of different colour temperatures.

 

Cross lighting using light sources of different colour temperature can create interesting colour effects as seen in the attached photo where natural light and incandescent light were involved.

 

I suspect that more than one lighting type may have been involved here:

http://s215.photobucket.com/user/PeterRatcliff/media/Ashmolean%20Exhibition/messiah_zps2f99dff6.jpg.html?sort=3&o=20

[Evan Smith]

Interesting photo.  Reminds me very much of what you get from fluorone dyes like the rhodamines.  Low energy reflected light is reddish, above the excitation threshold they emit brilliantly in the yellow.  Could something like that be happening here?  Anybody tried fluorones? 

Just wondering,,

Is there anything that you don't know something about,,,

or,,

is there something you don't know anything about?

 

 

[Evan Smith]

Seeing by eye direct is the only way to sense what's really going on, as Padding

explains in detail, the human eye has a built in exposure compensation and works with

the brain to produce an interpretation of what exists....that is what matters, not super high or 

super crap resolution debates. 

The inevitable 'here's my latest effort' photos bear that out and only eye to eye

can anyone really tell what is what. 

Bruce C generally has excellent photos to share and often explains them in context very well, 

hence his inclusion in the Padding book. Even there, eye to eye is best. 

:-)

This is true,,

maybe a video in stereo,,3-D might show it correctly.

[pbelin]

I've tried making fluorescent lakes, without success. The varnish is much more fluorescent than the pigments. But I'm not sure it's the solution. if the colouring matter becomes opaque (like varnish under black light) the whole effect is ruined.

Otherwise there would be lots of magical things to pick from Kremer's catalog!

[~ Ben Conover]

Padding's work, it's thorough. 
The analyses of his materials mentions green particles alongside the madder lake.
In the book there's a paragraph on Dichroism, basically he says it's in the wood. 
 

[Evan Smith]

Green and Red do make brown.

[Violadamore]

Just wondering,,

Is there anything that you don't know something about,,,

or,,

is there something you don't know anything about?

 

 

Why sure, but when this occurs, unlike some we see here, I choose to emit an expressive silence (or maybe a question). 

[Peter K-G]

In the book there's a paragraph on Dichroism, basically he says it's in the wood. 

 

 

I agree (as you see from my previous posts). Here just some more tests, one layer of clear varnish on top of the ground, these are all variants that can be seen in reality too:

 

 

Now I just have to do some color mixing without destroying this effect, but enhance it even more.

[Peter K-G]

Peter K-G, thanks for showing what I dismally failed in an earlier post. This is another try, moving the light and camera and using a neon-like tube bulb. It could be just light reflectance as Don suggested, but isn't light shift the alternate of the surface moving to create the change. I did put on another coat.

 

I think top wood is the challenge and I wish this is also shown in posts.

 

This is the challenge with spruce (I don't find spruce especially beautiful, but then again everything we build around here is with spruce or pine). The only way I can accept to enhance contrasts is time or lots of sunlight, everything else looks artificial. Never staining because it would make it look like the second image all the time.

[MikeC]

I think there is some confusion.    If we are talking dichromic or dichroic or whatever the correct term is.  It is not in the wood.  The only thing in the wood is reflectivity.  Anything other than natural wood color is in the coatings.   Wood color is  tan, beige, off white cream or whatever depending on oxidation and ageing and species. 

[Archiver]

I've tried making fluorescent lakes, without success. The varnish is much more fluorescent than the pigments. But I'm not sure it's the solution. if the colouring matter becomes opaque (like varnish under black light) the whole effect is ruined.

Otherwise there would be lots of magical things to pick from Kremer's catalog!

fluorescent pigment could be from sandarac resin

[pbelin]

Yes the resins we use are very fluorescent, in fact much more than any pigment I managed to make.

[Peter K-G]

I agree (as you see from my previous posts). Here just some more tests, one layer of clear varnish on top of the ground, these are all variants that can be seen in reality too:

 

 

Now I just have to do some color mixing without destroying this effect, but enhance it even more.

 

Just some more tests, now with thin varnish layer with pigments (madder mulled into the varnish). Second image, same light source:

 

[~ Ben Conover]

Resins are not florescent, it's the UV light which makes the ground of a classical 
varnish seem to be florescent, under the more opaque top layers. 

 

[FredN]

Hi John(post 50), because the reed (winter) lines are so sharply delineated I think the finish was created using an organic dye such as logwood, brazilwood, pernambuco, or others.  If an oil was used, or the 4:1 ros:oil ground coat that Nagyvary found in Cremonese inst's, the reed lines wouldn't be not be so thin and sharply defined. My guess.

[joerobson]

I think there is some confusion.    If we are talking dichromic or dichroic or whatever the correct term is.  It is not in the wood.  The only thing in the wood is reflectivity.  Anything other than natural wood color is in the coatings.   Wood color is  tan, beige, off white cream or whatever depending on oxidation and ageing and species. 

Mike,

I agree.  The discussion of dichromic/dicroiic appearances reminds me of the famous observation about pornography by Supreme Court Justice Potter Stewart...to paraphrase....I do not know how to define [it], but I know it when I see it. 

Magic Mike Molnar's Strad article addressed the issue well.  Attached is another way to explain wood and reflectivity.

on we go,

Joe

[joerobson]

I think there is some confusion.    If we are talking dichromic or dichroic or whatever the correct term is.  It is not in the wood.  The only thing in the wood is reflectivity.  Anything other than natural wood color is in the coatings.   Wood color is  tan, beige, off white cream or whatever depending on oxidation and ageing and species. 

Mike,

I agree.  The discussion of dichromic/dicroiic appearances reminds me of the famous observation about pornography by Supreme Court Justice Potter Stewart...to paraphrase....I do not know how to define [it], but I know it when I see it. 

Magic Mike Molnar's Strad article addressed the issue well.  Attached is another way to explain wood and reflectivity.

on we go,

Joe

SG05-wood.pdf

[MikeC]

That's a good PDF.  I think it was posted on an old thread that Don started on the subject of chatoyance.    Glad this thread got bumped as I've been searching for some old pics and just happened to find them on a defunct hard drive today.   Another entry in my journal of irreproducible results.   Excuse the green.  It's one of the rare times that I actually had any of that.  

Video to follow... if youtube cooperates.

[Michael_Molnar]

I think someone needs to do a movie of the view angle changing. This should show the effect better than a still photo.

[Marty Kasprzyk]

I think someone needs to do a movie of the view angle changing. This should show the effect better than a still photo.

Joseph Curtin did this with an Iphone.  He took pictures of the curly maple wood at various angles and then had them sequenced in the screen such that as you tilted the phone it looked just like you tilted the piece of wood.  The curls would show the light to dark color change as you tipped the phone back and forth. 

[MikeC]

I think someone needs to do a movie of the view angle changing. This should show the effect better than a still photo.

 

it would be nice to see a closeup video of an old Cremonese finish.

[Jim Bress]

I think someone needs to do a movie of the view angle changing. This should show the effect better than a still photo.

I remember Manfio showing a video moving a desk lamp back and forth over one of his viola backs.  I can even remember the sound of a squeak from a spring or hing on the lamp.  No time to search it out right now.  Maybe someone else will remember the thread it's in.  It might be in one of the old "what's on your bench" threads from before the contemporary maker's gallery.  However, his viola pictures are so incredible they give the impression of movement.  Lots of eye candy here http://www.maestronet.com/forum/index.php?/topic/327465-manfios-bench-my-latest-instrument/?hl=manfio 

 

-Jim

[Michael_Molnar]

I see that MikeC added a video to his still photos. Thanks, The point I was making is that makers should try to use videos to back up their claims of these optical effects. As Marty pointed out, video capability is now commonplace such as in iPhones. Still photos can be used if made in succession as the light angle is changed, but videos are better.

 

BTW, I am amazed with the  iPhone camera. It is superb.

[christian bayon]

I try but it is not easy, the IPhone get unfocussed when I move the violin.

IMG_2258.MOV

[MikeC]

For some reason it won't let me quote but anyway, the iphone camera is pretty good.   Both the stills and the video were done with my iphone.   In hindsight I should have done the video in indirect sunlight as the fluorescents wash out the color but that sample no longer exists.   Oh well... next time.  

 

That's a good video Christian.  I have trouble keeping the iphone in focus also though.