refractive index of varnish

[violins88]

I would like to measure the refractive index of my varnish. It looks to me like it is much easier to measure the IR of a liquid than a thin film solid. Does anyone know how much the IR changes as varnish dries? I am looking for simple, inexpensive, methods that do not require purchasing an instrument for $400 US.

Thanks in advance.

[Oded Kishony]

What are you going to do with this information?

first google hit: http://www.brooklyn.cuny.edu/bc/ahp/CellBi...ex/RI.Main.html

Another discussion for calculating the refraction index of a liquid which may apply to a thin film as well

http://www.physicsforums.com/showthread.php?t=133533

Oded

[Michael Richwine]

I would like to measure the refractive index of my varnish. It looks to me like it is much easier to measure the IR of a liquid than a thin film solid. Does anyone know how much the IR changes as varnish dries? I am looking for simple, inexpensive, methods that do not require purchasing an instrument for $400 US.

Thanks in advance.

The refractive index of most varnishes that contain linseed oil or shellac is in the 1.52 - 1.57 range. Are you trying to get a finer reading than that? To what end?

Gem refractometers can be had for around $100, but I doubt they would tell you more than you already know.

"Conservation of Furniture" by Rivers and Ulmney has a pretty good chart of the RI of common materials. You might want to see whether the library has it, because it costs $135. There's a pretty good discussion of coatings, pigments, and refractivity in there.

[violins88]

What are you going to do with this information?

first google hit: http://www.brooklyn.cuny.edu/bc/ahp/CellBi...ex/RI.Main.html

Another discussion for calculating the refraction index of a liquid which may apply to a thin film as well

http://www.physicsforums.com/showthread.php?t=133533

Oded

Oded,

I was hoping to find a high IR. Again, trying to see if my varnish is good or not.

I looked at both of those sites. Neither one works for a thin film.

Thanks, though.

[violins88]

The refractive index of most varnishes that contain linseed oil or shellac is in the 1.52 - 1.57 range. Are you trying to get a finer reading than that? To what end?

My assumption is that a higher IR is better. I really don't know if 1.52 to 1.57 have a noticeable effect on the look of the varnish. I assume so, but do not know for sure.

[Wm. Johnston]

My assumption is that a higher IR is better.

I tried some modern type varnishes, the one that looks the worst has an 'i.r.' of ~1.66 the one the looks best has an 'i.r.' of ~1.5

So why do you think bigger is better for a varnish's index of refraction?

Also I did intend to write 'i.r.' instead of i.r. there is more to the index of refection than just the numbers usually given. Some day if I have time I will write about this but for now it's homework time.

[MANFIO]

I'm quite bad in mathematics and I'm relatevly irrational with money but I've made this count:

Instrument for checking IR: 400

oil, resins and colorants

for tests till getting

a good varnish 1.000

precision scale 100

filters, recipients for cooking

varnish 100

working and studying hours value - let

me say, 200 hours for the project

for 10 dollars an hour: 2.000

TOTAL 3.600 dollars

suffient for getting top ready made varnish for the rest of your life. But I may be wrong and I'm one of those guys who cook varnish from time to time. And I may be wrong.

[joerobson]

I would like to measure the refractive index of my varnish. It looks to me like it is much easier to measure the IR of a liquid than a thin film solid. Does anyone know how much the IR changes as varnish dries? I am looking for simple, inexpensive, methods that do not require purchasing an instrument for $400 US.

Thanks in advance.

88,

The IR of an oil varnish is slightly higher then any of the constituent materials. Theoretically this is the same for the cured or uncured film.

Joe

[violins88]

88,

The IR of an oil varnish is slightly higher then any of the constituent materials. Theoretically this is the same for the cured or uncured film.

Joe

Thanks Joe.

[violins88]

I tried some modern type varnishes, the one that looks the worst has an 'i.r.' of ~1.66 the one the looks best has an 'i.r.' of ~1.5

So why do you think bigger is better for a varnish's index of refraction?

Also I did intend to write 'i.r.' instead of i.r. there is more to the index of refection than just the numbers usually given. Some day if I have time I will write about this but for now it's homework time.

Wm.

Actually, I guess the important thing is really that the IR of the ground match the wood IR and probably the varnish should match the Ground.

So, I guess you have access to IR measuring equipment. I am curious about the 1.66 varnish. What was the composition of that one?

Joe is the expert.

[violins88]

TOTAL 3.600 dollars

suffient for getting top ready made varnish for the rest of your life. But I may be wrong and I'm one of those guys who cook varnish from time to time. And I may be wrong.

Manfio,

and you apparently have been very successful. Thanks for all you posts.

[Michael_Molnar]

I learned in high school how to measure the refractive index of any medium using a microscope.

This is described here:

http://www.olympusmicro.com/primer/lightan...refraction.html

Have fun.

Mike

[arglebargle]

Oded,

I was hoping to find a high IR. Again, trying to see if my varnish is good or not.

I looked at both of those sites. Neither one works for a thin film.

Thanks, though.

Wouldn't the best measure of the quality of your varnish be,

in the end,

how it looked

and performed on your violin?

Why always chasing "magical" numbers and a scientific measure for what is

one of the most beautiful,elusive,and intriguing artistic duets around? A violin: it's creation, and it's use.

I don't know, but good luck with that i.r.

[Wm. Johnston]

So, I guess you have access to IR measuring equipment. I am curious about the 1.66 varnish. What was the composition of that one?

No equipment. This was a polyurethane varnish and it didn't look too good compared to a different varnish. The index of refraction was really just a guess and probably a little on the high side, based on values that I've found online.

The better looking varnish did have a lower index of refraction, around 1.5

[DBurns]

Does not Canada Balsam have a high Index of Refraction?

[violins88]

Wouldn't the best measure of the quality of your varnish be,

in the end,

how it looked

and performed on your violin?

Why always chasing "magical" numbers and a scientific measure for what is

one of the most beautiful,elusive,and intriguing artistic duets around? A violin: it's creation, and it's use.

I don't know, but good luck with that i.r.

Arglebargle,

"If the only tool you have is a hammer, every problem looks like a nail." I was trained in science, not art or music. There are two sides to this and both are right. How's that for weird logic?

Sam Zygmuntowicz was trained as an artist. But he has collaborated with a scientist, George Bissinger. For me, violin making is a good blend of art and science.

DBurns,

The IR of canada balsam is 1.54.

I found IR for cellulose to be 1.54 as well.

[violins88]

I learned in high school how to measure the refractive index of any medium using a microscope.

This is described here:

http://www.olympusmicro.com/primer/lightan...refraction.html

Have fun.

Mike

Mike,

Thanks for the link. Looks like your high school education was better than mine. Or maybe I should say, maybe you were a better student than I was. The good nuns did their best with me, but some of it did not "take."

[Selim]

Refractive index has a certain role in the refraction and reflection through thin films but it is rather the thicknes of the film and the wavelength that goes through, are important.

With Higher refractive index there is more chance for total internal reflection for a certain varnish thickness and wavelength of light(longer wavelenths).

[violins88]

I learned in high school how to measure the refractive index of any medium using a microscope.

This is described here:

http://www.olympusmicro.com/primer/lightan...refraction.html

Have fun.

Mike

Mike,

I found an error on that page (just bragging). The image of the prism, showing dispersion is wrong. Mistake

It should be this one.

And to Olympusmicro, you are welcome. You can send me a free refractometer to thank me.

[Oded Kishony]

Sam Zygmuntowicz was trained as an artist. But he has collaborated with a scientist, George Bissinger. For me, violin making is a good blend of art and science.

I'm not criticizing your interest in measuring the IR of your varnish though it's not how I would choose to go about it. However, for the sake of clarity, Sam doesn't depend on George Bissinger's data to determine if his violins sound good or not.

Oded

[Michael_Molnar]

Mike,

I found an error on that page (just bragging). The image of the prism, showing dispersion is wrong. Mistake

It should be this one.

... .

Good catch, John.

The paragraph on using the microscope is correct, nevertheless.

Mike

[violins88]

I'm not criticizing your interest in measuring the IR of your varnish though it's not how I would choose to go about it. However, for the sake of clarity, Sam doesn't depend on George Bissinger's data to determine if his violins sound good or not.

Oded

Oded,

Right you are.

[David Burgess]

So, back to the original question:

How can it be done with a thin varnish film?

[MANFIO]

I imagine it can be done by a trained naked eye, we know it's there when we see it on a good varnish, when we have the instrumen in our hands, but I may be wrong.

[Wm. Johnston]

So, back to the original question:

How can it be done with a thin varnish film?

If you have a polarizer then you can find the Brewster angle for light reflecting off the front surface of the film. The index of refraction can be found from the Brewster angle. To simplify the measurement you would probably want to put your varnish film on a non-reflecting backing. http://en.wikipedia.org/wiki/Brewster's_angle