Oil varnish sweating

[Dominik Tomasek]

50 minutes ago, HoGo said:

I remember someone posting varnish experiment with undiclosed thinner that gave such bad beading with the second coat...  Year or so ago... Who was it? Don Noon or Mike Molnar?

Yes that was Don's topic mentioned above. He had problems with thinner but it does not seem to by also my problem. 

[Dave Slight]

Rubbing down between coats can cause problems with adhesion, especially with stearate papers.

I suspect that your ingredients were not cooked correctly, at the right temperatures, or for the right length of time. As others have mentioned, tube oil paint can have a lot of oil, fillers and other undesirables, which will play havoc with the end result.

[Johnmasters]

On 1/8/2019 at 8:08 AM, joerobson said:

Several possibilities.

The most likely is that the varnish is not properly cooked so that the Linseed oil is not fully bonded with the resin.

Second is an issue with the amount of oil in the pigment you are using.

Try this:  take a papertowel and squeeze out a ribbon of the pigment on to the towel.  Let this sit for 24 hours in a warm place.

Excess oil will leech out on to the towel.

Joe

Joe,  do you think that this could be from out-gassing of some component  (Likely from the turpentine)  ?  I found to my chagrin on one repair,  that this happened,   and I thought I smelled mastic which has a high content of volatile "essential oils."

[Evan Smith]

On 1/6/2019 at 7:13 AM, Dominik Tomasek said:

Dear Maestronetters,

I have absolutely no idea whether "sweating" is relevant verb thus I am including some photographs. 

I have got this problem with my oil varnish - after it is applied it creates sort of tears, drops, lakes. My varnishing process is following - I prepare the surface, apply gelatine, than thin ground coat of my oil varnish (colophony, turpentine, linseed oil, lime), after it is dry I apply thin coat of artists' oil paint (colourant) and after the paint is dry I apply another coats of my cooked varnish. And then the problem begins. 

What could be wrong? I understand that some ingredient is drying faster than the other but why would it happen when the artists' paint is completely dry (even for several years)? 

Thank you in advance! 

Dominik

What kind of oil is in the artist oil paint?

Also it is best to not let the color coat completely dry before applying the next coat of varnish. It should be at the point of drying  that a bit of brushing will allow it to loosen up and start spreading around again. That way it will resolve and float in a layer in the varnish and not form a distinct layer and look like a layer of paint between coats of varnish. It can be tricky to do, it takes practice, timing is critical. Color it in several super thin coats instead of one thick one, thin color, thin varnish,, thin color  thin varnish, less is surely better. You can also add a bit of your varnish to the artist oil to increase compatibility, or put the artist paint into a jar of turp or whatever solvent you are using shake it up and let the pigment settle out, pour off the solvent then add the pigment to a small amount of your varnish to clean up the pigment and make it compatible. You can also add a bit of acetone or spike lavender or rosemary to your varnish to increase the wetting.

Many cheap drug store versions have fillers in them, It is best to use high quality artists oils for color, use high quality,,,Old Holland, Schmincke, Daniel Smith,,,, no safflower oil.

[FredN]

Hi Dominik, I've cooked  rosin with a saturated solution of calcium hydroxide wetted into crushed resin with umber pigment, cooked to dry, then added the oil for a final cook and never experienced  your problem. This makes me suspect the color coat or temperature of your cook. My cook is around 475oF for a few hours to where a drop on glass is no longer sticky when cool. Can you please describe the colored stuff and a little about cooking method.  thanks

[uncle duke]

On 1/6/2019 at 8:13 AM, Dominik Tomasek said:

 

The finish on the back plate here wants and needs spirits of turpentine to look right - to bumpy and rough.

About the belly plate - over the years I've mixed a lot of b.s. together to make an oil violin varnish.  I've never had the issue with sweating as it's called here.  Other than Don's suggestion of changing the thinner I'd firstly find ways to make what you want to use for a fnish without water being introduced into the mix anwhere.  I personally boil away any potential water from any solution that I think has water present.  Secondly I'd check the tube color msds to see what could possibly be causing a problem.  Make sure any brushes are clean and dry.

[joerobson]

On 1/9/2019 at 1:31 PM, Johnmasters said:

Joe,  do you think that this could be from out-gassing of some component  (Likely from the turpentine)  ?  I found to my chagrin on one repair,  that this happened,   and I thought I smelled mastic which has a high content of volatile "essential oils."

John,

Out gassing can cause such issues....based on poor quality turpentine. Have you tried this stuff?  http://www.diamondgforestproducts.com/~shop/list/?prdPerPage=5&catId=34919 

Essential oils can also do this to a poorly made varnish.  That's why I do not recommend Oil of Spike or Lavender any more.

on we go,

Joe

[Dominik Tomasek]

On 1/9/2019 at 11:56 PM, FredN said:

Hi Dominik, I've cooked  rosin with a saturated solution of calcium hydroxide wetted into crushed resin with umber pigment, cooked to dry, then added the oil for a final cook and never experienced  your problem. This makes me suspect the color coat or temperature of your cook. My cook is around 475oF for a few hours to where a drop on glass is no longer sticky when cool. Can you please describe the colored stuff and a little about cooking method.  thanks

Hi Fred,

to cook the varnish I melted 180 grams of colophony, into wich I added 10 grams of calcium hydroxide (lime) dissolved in about 30ml of water. Once the lime mixed with the colophony completely I poured in 180 mililitres of linseed oil and cooked the mixture for about one hour (the instructions told me to cook it for 30 minutes only but that was not sufficient). After one hour the varnish got darker thicker and had a decent string. I thought that one hour is not enough but since it was my first time cooking varnish I decided to stick to the instructions. After the varnish cooled a bit I added about 100ml of turpentine to thicken the varnish.

Regarding the colourant - it is oil based artists' paint I have no clue what are its ingredients. It is not stated on the tube. That leads me to the point where I think that this might be the problem... 

[Dominik Tomasek]

On 1/9/2019 at 8:18 PM, Evan Smith said:

What kind of oil is in the artist oil paint?

Also it is best to not let the color coat completely dry before applying the next coat of varnish. It should be at the point of drying  that a bit of brushing will allow it to loosen up and start spreading around again. That way it will resolve and float in a layer in the varnish and not form a distinct layer and look like a layer of paint between coats of varnish. It can be tricky to do, it takes practice, timing is critical. Color it in several super thin coats instead of one thick one, thin color, thin varnish,, thin color  thin varnish, less is surely better. You can also add a bit of your varnish to the artist oil to increase compatibility, or put the artist paint into a jar of turp or whatever solvent you are using shake it up and let the pigment settle out, pour off the solvent then add the pigment to a small amount of your varnish to clean up the pigment and make it compatible. You can also add a bit of acetone or spike lavender or rosemary to your varnish to increase the wetting.

Many cheap drug store versions have fillers in them, It is best to use high quality artists oils for color, use high quality,,,Old Holland, Schmincke, Daniel Smith,,,, no safflower oil.

Dear Evan,

thank you for you advices! These are my first instruments to varnish so...Long way to go I guess. 

I have no idea what is the composition of paints I am using, it would be better idea to buy high quality ones I would say. Well, next time I will know. 

Thanks

[Dominik Tomasek]

Right - I have got this little update:

I just varnished my viola. The steps were following: prepared surface, strong tea staining, gelatine applied. Then one coat of clear varnish. Once the varnish was dry I applied colourant on the back plate and put another coat of varnish. The result was nice, smooth and clear finish which I was satisfied with. Then I coloured the rest of the instrument and also gave it another coat over the colourant. This is still in the process of drying. But! Once I touched the already dry back plate (coloured and varnished) the sweating appeared! Absolutely confusing....

Dominik

[rudall]

> Once I touched the already dry back plate

What precisely do you mean by "touched"?

Andrew

[Dominik Tomasek]

Just now, rudall said:

> Once I touched the already dry back plate

What precisely do you mean by "touched"?

Andrew

I meant with the brush applying another coat of varnish.  

Sorry for not being exact. 

[David Burgess]

2 hours ago, Dominik Tomasek said:

Right - I have got this little update:

I just varnished my viola. The steps were following: prepared surface, strong tea staining, gelatine applied. Then one coat of clear varnish. Once the varnish was dry I applied colourant on the back plate and put another coat of varnish. The result was nice, smooth and clear finish which I was satisfied with. Then I coloured the rest of the instrument and also gave it another coat over the colourant. This is still in the process of drying. But! Once I touched the already dry back plate (coloured and varnished) the sweating appeared! Absolutely confusing....

Dominik

So this is happening with the next coat of varnish, after a layer of colorant and a layer of varnish have been applied? This might suggest a poor bond between the colorant and the varnish, such that brushing mechanical action (or softening from a solvent) allows the previous coat to come loose and "ball up" under the brush, leaving those high spots.

[David Burgess]

What you really should be doing though is sorting this out on test/sample pieces, so you don't get surprises and failures when varnishing the actual instrument. I can hardly emphasize this routine strongly enough.

[violinsRus]

What Burgess says above!  Right on the money.  Don't skip test pieces unless you are a glutton for punishment!

[Michael_Molnar]

I saw this sweating once many years ago and I think it was due to undercooked varnish. That is, the oil did not fully crosslink with the rosin. I imagine that you can get this if you blend too much uncooked oil into your varnish.  Maybe. 

In any case, remove the varnish and start fresh.

[Conor Russell]

4 hours ago, Dominik Tomasek said:

Right - I have got this little update:

I just varnished my viola. The steps were following: prepared surface, strong tea staining, gelatine applied. Then one coat of clear varnish. Once the varnish was dry I applied colourant on the back plate and put another coat of varnish. The result was nice, smooth and clear finish which I was satisfied with. Then I coloured the rest of the instrument and also gave it another coat over the colourant. This is still in the process of drying. But! Once I touched the already dry back plate (coloured and varnished) the sweating appeared! Absolutely confusing....

Dominik

So is it the already dry coat of varnish that's dissolving, or is it the the new coat that's  simply beading up on the surface?

I varnished  a cello some years ago, where the second coat brushed out  ok, but  ten minutes later had gathered  itself  up into lines and islands, leaving perfectly  bare patches several inches across.  I've no idea what was wrong, but I concluded the ingredients, or  the thinners,  must have been adulterated  with something  like a non drying oil.

I cleaned off the cello, washed it with acetone, dumped the varnish, and started again. 

If you rub down between  coats  you run the risk of contaminating the surface. And be careful  with  ingredients. Acetone sold as nail polish remover often has a moisturiser  mixed in for example, and if you wiped off the surface, or rinced a brush  with  it, you could  be in trouble. Likewise, isopropal alcohol  can have castor  oil  added, I think to stop people  from  drinking  it.

[David Burgess]

13 hours ago, Dominik Tomasek said:

Right - I have got this little update:

I just varnished my viola. The steps were following: prepared surface, strong tea staining, gelatine applied. Then one coat of clear varnish. Once the varnish was dry I applied colourant on the back plate and put another coat of varnish. The result was nice, smooth and clear finish which I was satisfied with. Then I coloured the rest of the instrument and also gave it another coat over the colourant. This is still in the process of drying. But! Once I touched the already dry back plate (coloured and varnished) the sweating appeared! Absolutely confusing....

Dominik

Could we please stop referring to this as "sweating",  since so far, based on your descriptions, the bumps don't seem to have anything to do with a liquid exudate from beneath.

If we can get that out of the way, the path can better be opened to more useful diagnoses.

[The Violin Beautiful]

How do you clean your brush? Is there any solvent residue on it that might be contaminating the varnish or reacting with your colorant?

[jezzupe]

Agree with David, if the "bumps" are not literally "wet" and are actually dry blisters, there is no mystery here at all, this is simply out gassing based on laying down too many coats with inadequate dry times in between....

breifly, the gelitine ground, depending on the cut, most likely will not give a satisfactory seal, and or can, on a microscopic level not create a monolithic shell that will span the gaps in all the cell openings, this allows the succeeding solvent base coat to fill into these pores. 

The problem then becomes relying on the "dry to the touch" declaration that it is "dry" and ready to be recoated. If the wood is then recoated with a second solvent base, as you describe, it will lay down, then start to dry, as it dries, it dries well over 99% of the surface, the "dry too touch surface" that it is adhering to, but what it is also doing is drying over pits and pores below the surface that act as "cups" that contain not completely dry varnish from the first solvent based coat.

Once this second coat has skinned over the first, the solvents from the first coat will start to evaporate out of the pores and then these areas start to act like little hot air balloons , inflating the skinned over second coat , in the solvents natural attempt to evaporate. Once this happens you get what you have your work showing, dried bubbles,pocks or nibblets...

IMO thats all nice fine and dandy, but you need to know what to do with it, imo I would not try to salvage this, I would whip out the turp rags and wipe it off, let it dry completely for several days, and then try again, giving more dry time in between coats...rely on your nose, not your hands for this, sniff the wood with your nose right on it, if you smell no solvent smell, then its good to go

edit' also, if you do wipe it off, make sure you deal with and dispose of those rags properly so as to not start a spontaneous combustion fire, of you don't know what "proper" is, read up on it.

[FredN]

 Hi Dominik- I think the problem is adding the oil before cooking out the water from the resin. I think the temperature is high enough when you go to cook out the water you also make a calcium soap. Calcium soap is similar to a sodium soap with which you wash  except it is barely water soluble, but it probably is hanging on to some water, or it is not soluble in the varnish mix and is congealing on to itself. The purpose of lime is simply to reduce the acidity of rosin, and really is not necessary for heat alone also does that, plus any metal you add. Jezzupe mentioned the possibility of gassing. Set up a bright light so that you can cast a shadow across the back, if the lumps sparkle they are gas filled. Solid ones usually don't. fred

[David Burgess]

40 minutes ago, FredN said:

 The purpose of lime is simply to reduce the acidity of rosin, and really is not necessary for heat alone also does that, plus any metal you add.

I have not yet found that heat alone will do that.

[Mike_Danielson]

It looks like you goofed up and contaminated it with something like silicones.   That has already been pointed out to you.  Strip the instrument with alcohol.  

Run tests on scrap pieces of wood to find out where the problem arises.

Here is the secret that the old guys know--coat with a thin shellac coat between varnish coats to act as a contaminant seal.  If you never find the problem, this will still work.

Mike D

[Dominik Tomasek]

On 1/11/2019 at 7:33 PM, jezzupe said:

Agree with David, if the "bumps" are not literally "wet" and are actually dry blisters, there is no mystery here at all, this is simply out gassing based on laying down too many coats with inadequate dry times in between....

breifly, the gelitine ground, depending on the cut, most likely will not give a satisfactory seal, and or can, on a microscopic level not create a monolithic shell that will span the gaps in all the cell openings, this allows the succeeding solvent base coat to fill into these pores. 

The problem then becomes relying on the "dry to the touch" declaration that it is "dry" and ready to be recoated. If the wood is then recoated with a second solvent base, as you describe, it will lay down, then start to dry, as it dries, it dries well over 99% of the surface, the "dry too touch surface" that it is adhering to, but what it is also doing is drying over pits and pores below the surface that act as "cups" that contain not completely dry varnish from the first solvent based coat.

Once this second coat has skinned over the first, the solvents from the first coat will start to evaporate out of the pores and then these areas start to act like little hot air balloons , inflating the skinned over second coat , in the solvents natural attempt to evaporate. Once this happens you get what you have your work showing, dried bubbles,pocks or nibblets...

IMO thats all nice fine and dandy, but you need to know what to do with it, imo I would not try to salvage this, I would whip out the turp rags and wipe it off, let it dry completely for several days, and then try again, giving more dry time in between coats...rely on your nose, not your hands for this, sniff the wood with your nose right on it, if you smell no solvent smell, then its good to go

edit' also, if you do wipe it off, make sure you deal with and dispose of those rags properly so as to not start a spontaneous combustion fire, of you don't know what "proper" is, read up on it.

From your describtion it seems that the problem could be the matter of not giving the varnish enough time to dry. The bumps really are sort of blisters or something. 

Thank you for your advice. 

[Dominik Tomasek]

16 hours ago, Mike_Danielson said:

It looks like you goofed up and contaminated it with something like silicones.   That has already been pointed out to you.  Strip the instrument with alcohol.  

Run tests on scrap pieces of wood to find out where the problem arises.

Here is the secret that the old guys know--coat with a thin shellac coat between varnish coats to act as a contaminant seal.  If you never find the problem, this will still work.

Mike D

Isn't there any risk of combining oil varnish and spirit thinne shellac?