violins88 Report post Posted March 8, 2009 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. Quote Share this post Link to post Share on other sites
Oded Kishony Report post Posted March 8, 2009 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 Quote Share this post Link to post Share on other sites
Michael Richwine Report post Posted March 8, 2009 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. Quote Share this post Link to post Share on other sites
violins88 Report post Posted March 8, 2009 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. Quote Share this post Link to post Share on other sites
violins88 Report post Posted March 8, 2009 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. Quote Share this post Link to post Share on other sites
Wm. Johnston Report post Posted March 8, 2009 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. Quote Share this post Link to post Share on other sites
MANFIO Report post Posted March 9, 2009 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. Quote Share this post Link to post Share on other sites
joerobson Report post Posted March 9, 2009 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 Quote Share this post Link to post Share on other sites
violins88 Report post Posted March 9, 2009 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. Quote Share this post Link to post Share on other sites
violins88 Report post Posted March 9, 2009 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 ~1.5So 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. Quote Share this post Link to post Share on other sites
violins88 Report post Posted March 9, 2009 TOTAL 3.600 dollarssuffient 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. Quote Share this post Link to post Share on other sites
Michael_Molnar Report post Posted March 9, 2009 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 Quote Share this post Link to post Share on other sites
arglebargle Report post Posted March 9, 2009 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. Quote Share this post Link to post Share on other sites
Wm. Johnston Report post Posted March 9, 2009 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 Quote Share this post Link to post Share on other sites
DBurns Report post Posted March 9, 2009 Does not Canada Balsam have a high Index of Refraction? Quote Share this post Link to post Share on other sites
violins88 Report post Posted March 9, 2009 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. Quote Share this post Link to post Share on other sites
violins88 Report post Posted March 9, 2009 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." Quote Share this post Link to post Share on other sites
Selim Report post Posted March 9, 2009 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). Quote Share this post Link to post Share on other sites
violins88 Report post Posted March 9, 2009 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. Quote Share this post Link to post Share on other sites
Oded Kishony Report post Posted March 9, 2009 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 Quote Share this post Link to post Share on other sites
Michael_Molnar Report post Posted March 9, 2009 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 Quote Share this post Link to post Share on other sites
violins88 Report post Posted March 9, 2009 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. Quote Share this post Link to post Share on other sites
David Burgess Report post Posted March 9, 2009 So, back to the original question: How can it be done with a thin varnish film? Quote Share this post Link to post Share on other sites
MANFIO Report post Posted March 9, 2009 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. Quote Share this post Link to post Share on other sites
Wm. Johnston Report post Posted March 9, 2009 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 Quote Share this post Link to post Share on other sites