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#1 Ken_N

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Posted 10 July 2008 - 05:45 PM

My varnish is still kinda tacky after 5 days. It had 2 nice days in the sun and the rest has been pretty humid and rainy. How long is too long? The first coat dried after one day and I varnished after 5 days. They only thing I did to the varnish is to add a small amout of red pigment and a little more linseed oil. Did that mess it up? Did the first coat sink into the ground, helping it dry, and I just have to be more patient? By the way I think it does look good! Its just not dry.

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#2 jonathan vacanti

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Posted 10 July 2008 - 06:30 PM

My guess is the linseed oil you added is the problem.

#3 joerobson

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Posted 10 July 2008 - 07:12 PM

My varnish is still kinda tacky after 5 days. It had 2 nice days in the sun and the rest has been pretty humid and rainy. How long is too long? The first coat dried after one day and I varnished after 5 days. They only thing I did to the varnish is to add a small amout of red pigment and a little more linseed oil. Did that mess it up? Did the first coat sink into the ground, helping it dry, and I just have to be more patient? By the way I think it does look good! Its just not dry.


Ken,
The first guess is definitely the linseed oil. How much did you add relative to the amount of varnish? Is it the same oil you used to make the varnish? What sort of varnish is it? What is the oil to resin ratio? What was the pigment?

Did you test the linseed oil prior to using it?
Let me know.
Joe

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#4 Andres Sender

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Posted 10 July 2008 - 07:13 PM

Was the linseed oil tested?

Oops, Hi Joe. :)
The problem with the ignore feature is that if one has a sort of morbid fascination for train wrecks one can keep peeking and then the benefit is out the window.

#5 Ken_N

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Posted 11 July 2008 - 03:05 PM

It was an old quart of boiled linseed oil I don't even remember buying, that was made in Canada. It has a $3.99 pric tag on it, that's how old it is. The first coat I cooked the oil with gum turps and resin and color and added it to the varnish. Maybe that made the oil better? I added about 10% oil maybe to the second coat. The pigment was some alizarin that was left at the bottom of a jar of the first varnish I mixed up that was just alizarin oil paint and the varnish. That stuff was nasty. Sticky, smeary color, just nasty. The finish looks nice, but it feels like sticky rubber. Not real tacky, Doesn't make fingerprints. Fingernails will sink in.

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#6 joerobson

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Posted 11 July 2008 - 07:25 PM

It was an old quart of boiled linseed oil I don't even remember buying, that was made in Canada. It has a $3.99 pric tag on it, that's how old it is. The first coat I cooked the oil with gum turps and resin and color and added it to the varnish. Maybe that made the oil better? I added about 10% oil maybe to the second coat. The pigment was some alizarin that was left at the bottom of a jar of the first varnish I mixed up that was just alizarin oil paint and the varnish. That stuff was nasty. Sticky, smeary color, just nasty. The finish looks nice, but it feels like sticky rubber. Not real tacky, Doesn't make fingerprints. Fingernails will sink in.

Ken,
Sounds like the film is not curing through. If you have a UV light box available, it may help. The linseed oil is the likely problem. The mixture of oil to the varnish changes its drying properties. Does it squeak but not move when you rub our thumb across it? Slip the inside of your wrist across the surface. What happens? Any noise? Any sticking?
Joe

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#7 Ken_N

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Posted 12 July 2008 - 06:53 AM

Well my thumb must be wetter. It doesn't move as easy, depending on how hard I push, and will squeak, even make the whole box resonate. My wrist slides easier and makes some noise, but not a squeak. It is humid again this morning so it seems stickier than when I just bring it in from out in the sun. It was just a thin layer I spread on with my fingers. I just noticed my other violin that has a top coat of the brown omega varnish drags a little on my wrist as well today, more on the belly where it has more texture. I even used my other wrist thinking some of the "stick" stuck to the wrist. The older one doesn't feel sticky though. If I press my had on the surface of the new one and then lift it off it sticks a little and makes some noise. The old one doen't do that on the back, but somewhat on the belly.

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#8 joerobson

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Posted 12 July 2008 - 08:03 PM

Well my thumb must be wetter. It doesn't move as easy, depending on how hard I push, and will squeak, even make the whole box resonate. My wrist slides easier and makes some noise, but not a squeak. It is humid again this morning so it seems stickier than when I just bring it in from out in the sun. It was just a thin layer I spread on with my fingers. I just noticed my other violin that has a top coat of the brown omega varnish drags a little on my wrist as well today, more on the belly where it has more texture. I even used my other wrist thinking some of the "stick" stuck to the wrist. The older one doesn't feel sticky though. If I press my had on the surface of the new one and then lift it off it sticks a little and makes some noise. The old one doen't do that on the back, but somewhat on the belly.


Ken,
If your thumb squeaks..a little... but the wrist slips, noise free, then the varnish should be dry enough to recoat. This varnish seems dry on the surface but not through the thickness. UV but minimal heat will help. Do you have a window with no direct sun? How about access to a UV box?

This situation is a pain in the butt...but correctable.
Joe

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#9 Ken_N

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Posted 12 July 2008 - 08:39 PM

Thank you for the tips and help. I have a lot to learn with lessons from the pros here at maestronet. Might as well do a lot of things wrong in the begining! Maybe there will be less on the next one. At least I might not have to strip that coat, it looks nice.

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#10 joerobson

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Posted 12 July 2008 - 09:04 PM

Thank you for the tips and help. I have a lot to learn with lessons from the pros here at maestronet. Might as well do a lot of things wrong in the begining! Maybe there will be less on the next one. At least I might not have to strip that coat, it looks nice.


Ken,
Let us know how this works out...you are not the only one to go through this problem.
Joe

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#11 HongDa

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Posted 12 July 2008 - 09:56 PM

It had 2 nice days in the sun and the rest has been pretty humid and rainy.

How's the temperature? Iv'e had similar problems when the humidity and temperature are both very high.

#12 ~ Ben Conover

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Posted 13 July 2008 - 08:21 AM

Linseed oil takes time to dry like said above, try a U.V. box or maybe you know someone with a greenhouse.

#13 Ken_N

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Posted 13 July 2008 - 08:38 AM

It's only been in the 80's so it's not too bad. I think it is more the humidity. Every morning there is fog coming off the ponds and streams. My basement is about 65 degrees and 65 humidity, feels good but it is too dark. My son's old reef tank light is burned out, or I'd try that. Maybe I can find a black light cheap somewhere. I have plenty of fixtures. I always thought that glass blocks uv light, so didn't think a window would work, unless it was opened.

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#14 ~ Ben Conover

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Posted 13 July 2008 - 09:09 AM

I think that glass trasmits U.V. but not plastic.

#15 David Burgess

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Posted 13 July 2008 - 10:20 AM

Ken, ordinary window glass blocks some UV, but also lets some through.

Unless you're running a dehumidier in the basement, or air conditioning, your basement humidity reading is suspect.

If you take outside air at 50% humidity and 80 degrees,and cool it to 65 degrees by moving it to your basement, the relative humidity becomes 84%. Cool that same air 5 more degrees to 60 degrees, and the humidity is 100%

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#16 Janito

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Posted 13 July 2008 - 10:31 AM

Ken, ordinary window glass blocks some UV, but also lets some through.

Unless you're running a dehumidier in the basement, or air conditioning, your basement humidity reading is suspect.

If you take outside air at 50% humidity and 80 degrees,and cool it to 65 degrees by moving it to your basement, the relative humidity becomes 84%. Cool that same air 5 more degrees to 60 degrees, and the humidity is 100%


Completely off topic, but the calculations of relative humidity have always fascinated me because they appear so counter-intuitive.

For example, why should changing the temperature make a jot of difference to the number of water molecules suspended in a given volume of 'air'?

If it is the number of water molecules that 'upsets' the oil varnish, why would the relative humdity matter?

Please excuse my naivite.

----------------
Ahhhh...increasing the temperature expands a gas, therefore there would be fewer water molecules in a given volume.

Am I on the right track?

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#17 Ken_N

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Posted 13 July 2008 - 10:47 AM

Janito, you have the relative humidity figured out.
David, I do have a dehumidifier in the basement. As you pointed out without it the basement would be useless. It is set at 60% but it is on a 6 hour on 6 hour off cycle so 65 is about as low as it has gone this year. I just guessed at those numbers. Just checked and it is 62 degrees and 68% humidity.

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#18 Ken_N

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Posted 13 July 2008 - 05:09 PM

I hung it all day in the shade side of a small cherry tree. It was dry and very windy and it seems dry now. Not 100%, but enough to put the fingerboard on and start setting it up.

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#19 Roland

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Posted 14 July 2008 - 08:36 AM

Completely off topic, but the calculations of relative humidity have always fascinated me because they appear so counter-intuitive.

For example, why should changing the temperature make a jot of difference to the number of water molecules suspended in a given volume of 'air'?

If it is the number of water molecules that 'upsets' the oil varnish, why would the relative humdity matter?

Please excuse my naivite.

----------------
Ahhhh...increasing the temperature expands a gas, therefore there would be fewer water molecules in a given volume.

Am I on the right track?


Hi Janito,

you are on the right track but it doesn't hit the nail on the head. First of all, we have to distinguish between absolute and relative humidity.

Absolute humidity is a concentration, its unit is amount of substance per volume, e.g. moles per cubic meter or gram per cubic meter.
Generally speaking, changing the temperature will usually have only slight effects on the absolute humidity. Assuming constant pressure, the absolute humidity actually decrease with rising temperature due to the expansion of gas (as you noted).

Relative humidity is defined as the actual concentration of water per maximal concentration of water in air. Therefore, it's dimensionless i.e. its dimension is unity (1). Water becomes increasingly soluble in air with rising temperature. In other words, the maximal concentration of water in air increases with temperature. On the other hand, lower temperatures lead to smaller maximal concentrations. Consequently, the relative humidity will rise with decreasing temperature when the absolute humidity is
kept constant. That is just the case David mentioned.

You asked why the relative humidity affects the drying process. Mass transfer depends on differences in concentrations. Large concentration gradients lead to fast mass transfer. A drying violin is a "source" of water which evaporates on its surface. Hence, the water concentration near its surface will (hopefully) be higher that the concentration of water in the environment. If the relative humidity is near 100 %, the resulting concentration differences will be small and lead to low mass transfer rates. As a result the drying process will take longer.


Hope this helps!

Roland

#20 David Burgess

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Posted 14 July 2008 - 10:56 AM

One quick thing to add to what Roland said:

One reason we're concerned more with relative humidity, rather than absolute humidity (total moisture content in the air), is that moisture content in dried wood tracks rather well with the relative humidity, given sufficient time to adjust.

Absolute humidity is more difficult to relate to wood moisture content and moisture transfer rates.

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