the effects of flatting agents on film clarity - Woodworking Talk - Woodworkers Forum
 
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post #1 of 14 Old 02-20-2012, 05:26 PM Thread Starter
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the effects of flatting agents on film clarity

Although these 200x micrographs were originally taken to show film blushing of nitrocellulose lacquer, It also shows most apparent the haze/milkiness/semi-opacity that is caused by agents used to lower the sheen of coatings. If you take this step further by using multiple coats of lower sheen material then it is even worse, thus my plea several times that building up finishes with many coats of flatted finish is unwise if one wants to maintain as much clarity of the finish as possible.

Now you may do a sample of this yourself just to see it's true, ready a sample board apply a couple of coats of black let dry and the tape off in 2 sections spray one with a couple of coats of gloss the other with say satin, let dry and view you will readily see how much more milky/hazy the satin looks in comparison, and also how much greyer and less black, on lighter finishes it does not show up as much to be sure, but it is still there and takes away from the depth of clarity the gloss has, so i continue to suggest and implore you to at least build your finish with gloss and only apply the last coat of finish if needed as the flatted coat ok?
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post #2 of 14 Old 02-21-2012, 12:54 PM
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I agree! I was told by my finish supplier that flattening agents also make for a softer surface that scratches easier.
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post #3 of 14 Old 02-21-2012, 01:12 PM
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Originally Posted by chemmy View Post
Although these 200x micrographs were originally taken to show film blushing of nitrocellulose lacquer, It also shows most apparent the haze/milkiness/semi-opacity that is caused by agents used to lower the sheen of coatings. If you take this step further by using multiple coats of lower sheen material then it is even worse, thus my plea several times that building up finishes with many coats of flatted finish is unwise if one wants to maintain as much clarity of the finish as possible.

Now you may do a sample of this yourself just to see it's true, ready a sample board apply a couple of coats of black let dry and the tape off in 2 sections spray one with a couple of coats of gloss the other with say satin, let dry and view you will readily see how much more milky/hazy the satin looks in comparison, and also how much greyer and less black, on lighter finishes it does not show up as much to be sure, but it is still there and takes away from the depth of clarity the gloss has, so i continue to suggest and implore you to at least build your finish with gloss and only apply the last coat of finish if needed as the flatted coat ok?
Oke Doke I'm sold.
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post #4 of 14 Old 02-21-2012, 04:21 PM Thread Starter
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Originally Posted by MNsawyergp View Post
I agree! I was told by my finish supplier that flattening agents also make for a softer surface that scratches easier.
Actually the most common flatting agent is silica [fumed silica] that is pretty hard. there are others such as polyethylene waxes and amides, but are not used as much, but on the rise.

I think what he might have meant, and you can ask again, is that the material used in sanding sealers are softer and scratch white of course which is true.

The reason i state this is whatever flatting agent [FA] is used except for amides, or other fatty like resinous materials, they are embedded in the finish for the biggest part, meaning little is on the surface to be scratched. They are heavier that the resin coating and therefore sink and accumulate at the bottom or within the film.

Think of it this way, as the film dries it shrinks and the FA particles are sandwiched in the layer[s] but all of the FA particles are covered with the film coating, they are not laying on top of the film exposed to the air or environment. of course this can only be seen under microscopy, but never the less is true. So if it's only the "film" on the surface, how can it be easier to scratch than the same film that has no FA ???

Just ask again to be sure what he meant and if he is still adamant then explain what i said here and get back ok? maybe he knows something i don't, lol.

Get my point?
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post #5 of 14 Old 02-21-2012, 04:31 PM
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Want to make the surface clear again? Here's how.

All of the deglossing that occurs when using a finish containing flatting agents is on the top surface of the last coat applied. The following is from a write up I did a few years ago for a woodworking club newsletter. The issue came up again recently on the finishing forum of another website and I have copied my response on that site. The original statement on that site was "Applying gloss sheen (no flatting agents) over a dull sheen will not produce a high gloss finish since the flatting agents in the dull (or duller) finish are still there. My response follows:

Steve the original writer, I hate to pick a nit but I do not believe the above is correct. A few years ago I wrote up the following for woodworking club newsletter. The most recent edition of Flexner's book Understanding Finishing has a section on the same subject arriving at the same conclusions.

The additive used by most finish manufacturers is a silica (glass) that is optically clear. Compare a well stirred satin finish to a gloss finish and you will see little or no difference in clarity.

The way the flatters work is that as a finish dries, it shrinks slightly. This pulls the top of the film tighter causing the granular sand-like silica items to make the surface un-smooth. It's the non-smooth surface that refracts and scatters the light rays giving the appearance of a non-gloss finish. The whole effect of the non-gloss is only at the surface of the finish. If you apply a second coat, the hills and valleys of the underneath coat are filled in and the drying of the new coat again creates new hills and valleys at the surface of the new coat. If you apply a gloss finish (which has no flatters) it too will fill in the hills and valleys in the prior coat but no new hills and valleys will be created. You are left now with a gloss finish even though the underneath coat was a non-gloss.

Think about scuff sanding a surface as preparation for applying another coat of finish. The scuff sanded surface will have a non-gloss appearance because of the scratches (hills and valleys) that the abrasive material creates. But, what happens when you apply another coat of gloss to your scratched surface? The resulting new surface is gloss because your gloss finish has filled in the scratches just like it does to the hills and valleys resulting from a non-gloss finish.

So, what should be taken away from this overly long dissertation is that for almost all finishes used in woodworking, it makes no difference what the gloss of the underneath coats are or were, the final gloss will be dependent on the gloss of the final coat.

A question was asked: >>>> The silicates do refract light to some degree, don't they?

Yes they do, but only at the surface where the shrinkage has created the non-smooth surface. As I said, there is no difference in the scattering of the light created by flatting agents and the scattering of the light created by sanding or otherwise roughening of the surface. If a gloss finish is applied over either roughened surface, the end result of a gloss finish is the same.

Well, you have forced me to get out my copy of Flexner's Understanding Wood Finishing. On pages 110-111 in his latest edition he covers this subject. The article also contains diagrams and photos illustrating the points I made.

Flexner's conclusion is the "given that the silica flatting agents are optically clear, within a reasonable and normal film thickness, there will be no affect on clarity.

So, as an experiment, apply a clear gloss finish over a non-gloss part of your sample board and lets see what happens.

Howie..........
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post #6 of 14 Old 02-21-2012, 07:39 PM
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Originally Posted by HowardAcheson View Post
Want to make the surface clear again? Here's how.

Flexner's conclusion is the "given that the silica flatting agents are optically clear, within a reasonable and normal film thickness, there will be no affect on clarity.

.

Strange, it appears he says that small amount of light scattering does not produce opacity? (NO effect on clarity?)

In other words, adding a little bit of pigments do not make a coating less transparent?

If the Refractive Index of the silica is EXACTLY the same as the varnish than perhaps he is right, but RI matching is not quite that simple.

A quote from a post by a Phisicist. ( I hope he does not mind, it's in a forum)

"First, the index of refraction isn't just a constant for a material. It varies with the wavelength of the light....

.....Second, the index of refraction is not just one number. The index of refraction is one complex number which is really two numbers! See this, http://en.wikipedia....efractive_index go down to the dispersion and absorption section. The 'real' part of the index of refraction is the number often quoted as the 'index of refraction' but it's really just half of it. The so called 'imaginary' part of the index of refraction gives rise to the absorption of light. The imaginary part of the index of refraction is directly related to the absortion coefficient that I have brought up in other varnish discussions. The imaginary part of the index of refraction gives rise to the color and opacity present in varnishes.

Now an important thing to keep in mind at wood/varnish or varnish/air interfaces is that if you want to deal with reflection and transmission at that boundary you should use the complex index of refraction not just the single number often quoted (if you are plugging into the Fresnel equations). ...."

Wm. Johnston

I'd like to see a sample of varnish with flatting agents and last coat without, side by side with one without flatting agents, on top of glass, and compare....

Last edited by Carlo Bartolini; 02-21-2012 at 08:07 PM.
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post #7 of 14 Old 02-21-2012, 08:35 PM Thread Starter
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Howie, if your talking of just the sheen being gloss again by using your methods, that is true. Applying a coat of gloss and then measuring it with a 60 or 20/60 80 degree gloss meter will read in the high 80's to possibly the low 90's, this would be true for almost all gloss coatings, that are applied that are at least a half mil thick or more. Even then a few coatings would still read in this range.

But if your meaning to say the "haziness" would be gone or eliminated then you are incorrect and so is Flexner if he is in agreement or your in agreement with him.

Though a portion of the silicates are just beneath the coating surface there are more lying underneath of them, how the upper ones lay once sprayed on, creates the differing refractive angles that cause the the "appearance" of a less gloss surface. the upper ones do most of this, but the ones under them contribute to the haziness.

Though you say that the silica is clear and rightfully so, it is clear only to the degree it is not interfered with by other silica layers over top of each other, if it were crystal clear it would not be seen as it is in the container or poured out into a glass beaker, just as much as fine pumice or Tripoli looks clear when mixed with shellac and alcohol and applied as a pore filler in french polishing looks clear to a large degree, when in the pores, it does not appear that way when in bulk condition within the coating before application.

But when you enlarge the particles at fairly high magnification when wet and placed on a slide of black glass, you can easily determine that there is no pure clarity to them, they still have some slight opacity or should i say tran"lusence" to them when piled on top of each other.

Since we are talking of hundreds of thousands of particles per gallon or more, it is much amplified over a small amount in gloss range, dead dead flat 5 sheen, through dead flat/flat/low satin/satin/high satin/semi-gloss, or 10/20/30/40/60/80 sheen's respectively, the more silica the more haziness because the particles are closer together.

When at OSF America as finishing supervisor i was first asked to look at the coatings that were coming from the main plant in Ontario to see if I could tell them how to rid the milkiness, from the darker finishes especially, that were being produced. they had been using satin 30 sheen 2K polyurethane to build several coats up on their table tops and looked hazy as hell. Now the finish itself was as glossy as could be, rubbed out to perfection, just like liquid glass, very impressive!

the reason they were building with satin was to avoid having to have many different sheens on hand since this was no small operation 2 hundred million a year with 12% of that in finishing material cost, So when the original sample was made the determination was also made just to finish them with the satin with no regard as to any milkiness. The correct thing to do of course would have been to finish them all with gloss, which of course was my immediate answer.

so even though your correct as to the refraction of light caused by the upper layer of silica laying at differing angles overlapping each other, the finish itself still becomes hazy/milky/translucent, to varying degrees. This is what i talk of here. it's not that your incorrect per say it's that your only addressing one facet of what is happening, such as many people do.

Since you ask others to do samples i will do the same, a simple test as to what I'm trying to get across with my micro photos ok?

Take a piece of clear glass, spray a coat of the glossiest black you can find on one half, allow to dry and mask off and then spray the remaining side and let dry, to be sure, make certain to let them over lap a little so that there are no "clear glass" gaps in between the two ok? now, since the reverse side is nice and smooth and glossy as "glass" and one could do no better if clear gloss of any kind, simply turn it over and view, you will see that the high black gloss coating still looks very high gloss and also that from the outer glass surface appearance so does the flat black, but then next you will plainly see that though it is glossy in that sense, it too also looks milky hazy as compared to the glossy black in the sense I'm talking of.

Second test: do the same thing now with clear coating materials, say acrylic, which is the clearest one, and when dry hold up to the light, you will plainly see that the acrylic flat finish - even though it is gloss when looking from it on the non coated glass side, readily appears hazy and with each successive coat it will again look more hazy, with several coats even more so, etc.

Third test : take the same pain of glass you put the clear flatted finsh on and now apply another wet coat and then sandwhich it with another piece of glass, you will see even though both sides now are gloss glass that the film remains hazy!

My point? Even though your methods or others methods to show what you mean may be facetedly true, it does not take away the "fact" that flatted finishes cause haze/milkiness/light opacity/translucency, frostyness, and that takes away from the depth and clarity of any wood finish. Think of this as another example, maybe you or someone in the family has used what is called frosting at christmas time to sray on windows, what do you think that clear flat finish is that makes the glass look frosted "from either side of the glass?

That is why my advice to build with gloss only, and if needs be, only apply a final coat of flatted finish or hand rub if you must.

It's not the flatted look thats bothersome to me or most others, its the haziness/frostyness,.

Last edited by chemmy; 02-22-2012 at 11:00 PM.
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post #8 of 14 Old 02-21-2012, 09:34 PM
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Thanks a lot

Early on I was convinced I had learned me sumpin bout making my creations look sharp. Now I don't want to build anything because I am nervious about going to the store for varnish. I don't even know what to ask for and fear the guy at the paint store might explain and I will not be able to put all the information to use.
Mi cabeza meduele y es necesario establecer.
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post #9 of 14 Old 02-21-2012, 09:40 PM
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Boy theres lots of good info hear, im learning a lot.
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post #10 of 14 Old 02-22-2012, 05:19 PM Thread Starter
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Originally Posted by Carlo Bartolini View Post
Strange, it appears he says that small amount of light scattering does not produce opacity? (NO effect on clarity?)

In other words, adding a little bit of pigments do not make a coating less transparent?

If the Refractive Index of the silica is EXACTLY the same as the varnish than perhaps he is right, but RI matching is not quite that simple.

A quote from a post by a Phisicist. ( I hope he does not mind, it's in a forum)

"First, the index of refraction isn't just a constant for a material. It varies with the wavelength of the light....

.....Second, the index of refraction is not just one number. The index of refraction is one complex number which is really two numbers! See this, http://en.wikipedia....efractive_index go down to the dispersion and absorption section. The 'real' part of the index of refraction is the number often quoted as the 'index of refraction' but it's really just half of it. The so called 'imaginary' part of the index of refraction gives rise to the absorption of light. The imaginary part of the index of refraction is directly related to the absortion coefficient that I have brought up in other varnish discussions. The imaginary part of the index of refraction gives rise to the color and opacity present in varnishes.

Now an important thing to keep in mind at wood/varnish or varnish/air interfaces is that if you want to deal with reflection and transmission at that boundary you should use the complex index of refraction not just the single number often quoted (if you are plugging into the Fresnel equations). ...."

Wm. Johnston

I'd like to see a sample of varnish with flatting agents and last coat without, side by side with one without flatting agents, on top of glass, and compare....
Hi Carlo, well.. there are exceptionally clear silicone dioxides that are used on or as flatting agents. there micron size runs between 3-9 microns and the purity is 99+%, That said, my point is that even when you lay thin layers of opticlly clear glass on top of each other at varying angles of light incedence, you create an effect that visually dulls the natural gloss of the glass, if you were to look into a jar full of perfectly clear minute flat glass crystals that were optically clear, they would appear frosty, unlike if you were to lay each one out side by side. If there were no frostyness the fact is that it would not perform the job it's intended to do, which is reflect the light at differeing angles to break up the appearence of the gloss coating. that said, even larger or smaller particles would do the same ok?

The simplest question to ask common sense wise would be - "why use something to flatten or lower the gloss if it would not have the ability or properties to do so, what purpose would it then serve?? you might as well just use liquid glass if that's the case.

Though you could use and sometimes was or is done "fumed silica which is anything but clear [see wiki for pics] the idea is to not frost up the material anymore than is necessary. though fumes silica is used for thixotropic purposes, it is more in the realm of pigmented coatings than clears. Now with the new nano particles we will have to wait and see if any improvements are worth switching to. doubtful only because it will still have to have the same abilities. Though if cheaper, hmmm?

i've included a few pics of the behavior of solvent used with glass beads that have not been polished and how it affects the clarity of or on the beads, it may be of interest. Of course this has to do with the RI values not the flatting values, but the best way to insure more frosted appearences is to have the solvent and or coating line up less with the index of that which it is applied to ok?

A) is showing glass bead in air refraction only, Refractive index [N/d of air N/d = 1,

B) is in a solvent/liquid with somewhat higher N/d, you can see better transparency,

C) has a higher RI, D) RI over 1.4,

D) is in a liquid with a N/d of 1.67, much more trasnparency,

unfortunately they did not go up to 1.7-8 it would have looked clearer still.

Therfore the solvents/resins in coating would give the silica enough frostyness to obscure the substrate to the varying degree we see ok?
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Last edited by chemmy; 02-22-2012 at 10:37 PM.
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post #11 of 14 Old 02-22-2012, 06:48 PM
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Just ask again to be sure what he meant and if he is still adamant then explain what i said here and get back ok? maybe he knows something i don't, lol.
How can that be?






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post #12 of 14 Old 02-22-2012, 07:05 PM Thread Starter
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How can that be?









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For everything i know there is a million i donot C'man. don't be a hater ok
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How can that be?









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C-Man, did my sarcastic Yankee humor rub off on you?
BTW, how have you been?

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post #14 of 14 Old 02-26-2012, 04:31 PM
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C-Man, did my sarcastic Yankee humor rub off on you?
BTW, how have you been?
I thought mine rubbed off on you. Actually I'm OK as long as I keep eatin' my spinach.






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