Oil Varnish


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On 8/27/2018 at 5:17 PM, joerobson said:

A note from a varnish geek:

Linseed oil cooked long enough at the proper temperature gradient when cooled will form a gel dense enough to be cut into cubes.  This was used to polish patent leather shoes. 

on we go,

Joe

Or to catch birds.

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On 08/27/2018 at 12:17 PM, joerobson said:

A note from a varnish geek:

Linseed oil cooked long enough at the proper temperature gradient when cooled will form a gel dense enough to be cut into cubes.  This was used to polish patent leather shoes.

on we go,

Joe

Hi Joe,

Would the dense gelled linseed oil make a good wood sealer/filler?  It couldn't soak in very far because of its high viscosity--just rub it on and polish it like done on leather shoes?  Then put normal varnish on top of it?

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2 hours ago, Marty Kasprzyk said:

Hi Joe,

Would the dense gelled linseed oil make a good wood sealer/filler?  It couldn't soak in very far because of its high viscosity--just rub it on and polish it like done on leather shoes?  Then put normal varnish on top of it?

I am afraid, such a high-viscosity gel could be quite sticky - not a nice procedure to remove the rests from the wood-surface,  however possible. 

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17 minutes ago, Danube Fiddler said:

I am afraid, such a high-viscosity gel could be quite sticky - not a nice procedure to remove the rests from the wood-surface,  however possible. 

Depends on what you mix into it...

I once had old bottle of Tru-oil (it's kind of polymerized linseed oil with small amounts of resin added) that was completely gelled. I just scooped it out of the bottle and used as sealer on old fiddle - worked excellently. I put a piece on rag and rubbed it into and off the surface and got beautiful satin sheen surface on which I applied colored varnish.

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On 8/27/2018 at 6:46 AM, FredN said:

Nick, from experience pulling a long string often is deceptive and the varnish will take a longer time to dry than expected. I gave up on it and use heat to get a steady surface foam, even just a thin rim foam, and stop cooking when the foam starts to go away. A thin rim foam leaves you at the  off-and-on vagaries of your heat plate, using a surface foam overcomes this.  

Fred, 

 

if if you are cooking colophony at a low temp to archive maximum colouring without burning and producing carbon in your varnish, wouldn’t raising the temperatures to achieve the foam just end up burning the rosin you carefully cooked at a low temperature? How hot are you talking?

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22 minutes ago, HoGo said:

Depends on what you mix into it...

I once had old bottle of Tru-oil (it's kind of polymerized linseed oil with small amounts of resin added) that was completely gelled. I just scooped it out of the bottle and used as sealer on old fiddle - worked excellently. I put a piece on rag and rubbed it into and off the surface and got beautiful satin sheen surface on which I applied colored varnish.

Sounds good ! May be, only a little bit of resin can catch the stickyness of a thickened linseed oil, if it should have it at all. May be this was the ground, Echard et al had found. 

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8 minutes ago, David Burgess said:

It won't stay that way, but will continue to harden.

Did you ever see a completely hard layer of pure linseed oil ( that means without resin ) ? 

Since I have read of a re-softened poppy-seed-oil layer in a famous painters textbook ( Doerner or Wehlte ) my personal assumption is, that in dried oil-layers generally could be something like a balance of hardening and softening processes. May be the balance-points change very slowly into the more harder direction - normally. However the whole oil-drying thing is according to wikipedia infos chemically/technically not completely understood.

In a little bottle with sun-thickened linseed oil, the oil seems to be extremely high-viscous - until I turn it some few times - after this it is much lesser high-viscous. I speculate, what happens in the course of centuries while playing the instruments, within the linseed-layers.......

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Hi Finn- I bring the mix to a 1/4 inch rim foam which I think is around 500F.  All contents are being cooked at the same time, rosin, oil, umber as a colorant and drier, so any color contributed by the rosin is mixed in.  Literature states rosin and oil should be cooked together because there is an interchange between resin and oil. Doesn't describe the reaction. fred

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On 9/17/2018 at 3:49 PM, finnfinnviolin said:

Fred, 

 

if if you are cooking colophony at a low temp to archive maximum colouring without burning and producing carbon in your varnish, wouldn’t raising the temperatures to achieve the foam just end up burning the rosin you carefully cooked at a low temperature? How hot are you talking?

You are not adding carbon to the varnish. You are oxidizing it similar to toasting bread. If you toast bread too far, you turn it into carbon and it looks, smells, and tastes terrible. Burnt varnish has black opaque clumps that destroy the varnish. Cooking pots that have hot spots on the bottom are notorious for burning. 

IIRC, the foaming temperature is about 290 C. Would someone check if that is right.

Roasting rosin is at a much lower temperature, a little above 200 C. Again, someone should check my figures. 

Edited by Michael_Molnar
Fixed and changed to 290C.
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1 hour ago, Michael_Molnar said:

You are not adding carbon to the varnish. You are oxidizing it similar to toasting bread. If you toast bread too far, you turn it into carbon and it looks, smells, and tastes terrible. Burnt varnish has black opaque clumps that destroy the varnish. Cooking pots that have hot spots on the bottom are notorious for burning. 

IIRC, the foaming temperature is about 390 C. Would someone check if that is right.

Roasting rosin is at a much lower temperature, a little above 200 C. Again, someone should check my figures. 

Right, but I have cooked colophony in two different ways, one at low temp, one at high, the one at high temp has to be sat on a shelf for a year or so so that the crud and carbon particles sink to the bottom, what I’m saying is that this seems pretty high to me, and I wonder if cooking this high when getting to the pill stage could possibly burn your rosin.

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5 hours ago, HoGo said:

Depends on what you mix into it...

I once had old bottle of Tru-oil (it's kind of polymerized linseed oil with small amounts of resin added) that was completely gelled. I just scooped it out of the bottle and used as sealer on old fiddle - worked excellently. I put a piece on rag and rubbed it into and off the surface and got beautiful satin sheen surface on which I applied colored varnish.

Thanks HoGo!  You're way ahead of me.

I use Tru-Oil too and have had problems with the oil gelling in old bottles that had been opened but were only partially used.  I was wondering if the gel was useful as a filler.  I would guess it would harden just as well as fresh oil.

Since the gelling is happening in a dark and opaque bottle I assume it is happening due to air exposure rather than from light exposure.

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7 hours ago, Marty Kasprzyk said:

Thanks HoGo!  You're way ahead of me.

I use Tru-Oil too and have had problems with the oil gelling in old bottles that had been opened but were only partially used.  I was wondering if the gel was useful as a filler.  I would guess it would harden just as well as fresh oil.

Since the gelling is happening in a dark and opaque bottle I assume it is happening due to air exposure rather than from light exposure.

Same happening here, once the bottle catches oxygen it will thicken. I removed the hard rubbery skin and the part that I used was soft jelly consistency. I rubbed it on and off and got smooth sealed surface in one go...  I applied few "glaze" coats of oil varnish (I believe I used copal varnish I cooked when I was a bit braver) and transparent madder and umber oil paints with fingers over that sealer and the finish is in fine shape now, some 20 years later, no peeling, cracking or other bad effects.

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9 hours ago, finnfinnviolin said:

Right, but I have cooked colophony in two different ways, one at low temp, one at high, the one at high temp has to be sat on a shelf for a year or so so that the crud and carbon particles sink to the bottom, what I’m saying is that this seems pretty high to me, and I wonder if cooking this high when getting to the pill stage could possibly burn your rosin. 

I think the darkening of the colour is a kind of burning the rosin. I can't see an oxidisatino process that would change the colour in the same way. The burn fraction is probably small and may have a desirable effect on colour. But some of it is probably not abietic acid any more.

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11 hours ago, Danube Fiddler said:

Did you ever see a completely hard layer of pure linseed oil ( that means without resin ) ? 

 

Yes. The  "plateau" in the drying curve that I mentioned in another thread isn't completely horizontal. It continues to rise with light exposure, but at a much slower rate.

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9 minutes ago, David Burgess said:

The  "plateau" in the drying curve that I mentioned in another thread isn't completely horizontal. It continues to rise with light exposure, but at a much slower rate.

This I also would have expected.

11 minutes ago, David Burgess said:

Yes. 

Found in your own experiments with resin-free linseed oil ? - with a comparable hardness like e.g. a sandarac-raw-resin or even like glass ?

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17 hours ago, finnfinnviolin said:

Right, but I have cooked colophony in two different ways, one at low temp, one at high, the one at high temp has to be sat on a shelf for a year or so so that the crud and carbon particles sink to the bottom, what I’m saying is that this seems pretty high to me, and I wonder if cooking this high when getting to the pill stage could possibly burn your rosin.

I would throw out the cooked rosin that has charcoal particles. Life is too short. It's a mystery to me why the addition of linseed oil permits cooking at such a high temperature. Pure rosin burns, but not varnish. Perhaps, he crosslinking helps. Maybe Fred or Joe could shed some light on this.

BTW, everything I told you works for me, so give it a shot. 

Be careful of hot spots on the pot bottom.

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8 hours ago, Danube Fiddler said:

This I also would have expected.

Found in your own experiments with resin-free linseed oil ? - with a comparable hardness like e.g. a sandarac-raw-resin or even like glass ?

Yes, in my own experiments. No, not the same hardness as some resins, or glass.

42 minutes ago, Michael_Molnar said:

Be careful of hot spots on the pot bottom.

Yup. Hot spots can take localized temperatures way above those measured with a thermometer. These can be reduced by using a very thick pot which spreads the heat more evenly, or using a sand bath. My current method is to heat evenly from all sides using an oven.

Warning: You will need a "chimney" to extract the volatile exudates, because they can catch fire or explode.

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On 9/17/2018 at 9:50 PM, Michael_Molnar said:

You are not adding carbon to the varnish. You are oxidizing it similar to toasting bread. If you toast bread too far, you turn it into carbon and it looks, smells, and tastes terrible. Burnt varnish has black opaque clumps that destroy the varnish. Cooking pots that have hot spots on the bottom are notorious for burning. 

IIRC, the foaming temperature is about 390 C. Would someone check if that is right.

Roasting rosin is at a much lower temperature, a little above 200 C. Again, someone should check my figures. 

The melting point of abietic acid is around 175˚C. A 'foaming point" is not a chemical property. Melting = boiling. This will be lowered by imputities (ebullisocopic propertes).

If you slowly change colour you get all kinds of oxidisation products, unlikely carbon. If you really burn it you end up with residues of what is there besdies abeitic acid and some tar like long chained products, besides CO2 (in the presence of oxygen).

Some  slowly oxidised rosin can have very desirable colours for varnish. If I ready Hargrave's bass article correctly he colours his varnish just this way or by adding a little nitric acid.

However 200 ˚C is certainly enough for all of this.

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4 hours ago, David Burgess said:

Yes, in my own experiments. No, not the same hardness as some resins, or glass.

Yup. Hot spots can take localized temperatures way above those measured with a thermometer. These can be reduced by using a very thick pot which spreads the heat more evenly, or using a sand bath. My current method is to heat evenly from all sides using an oven.

Warning: You will need a "chimney" to extract the volatile exudates, because they can catch fire or explode. 

Chemists would use an electrical heating mantel. But this does not distribute heat evenly, nor does a sand bath. You also need a magnetic stirrer to keep temperature exposure more even. All of this seems an overkill, I can't see classical makers using anythong but a wood fire, maybe an oven, but without any temperature control.

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17 hours ago, uguntde said:

The melting point of abietic acid is around 175˚C. A 'foaming point" is not a chemical property. Melting = boiling. This will be lowered by impurities (ebullioscopic properties).

 

 

The "foaming point" reaction that Fred mentions is for making varnish, namely crosslinking the rosin and oil, and not for roasting rosin. I have experimented with this and confirmed that I see it around 290 C. 

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29 minutes ago, Michael_Molnar said:

The "foaming point" reaction that Fred mentions is for making varnish, namely crosslinking the rosin and oil, and not for roasting rosin. I have experimented with this and confirmed that I see it around 390C. 

You did say an experiment right?..........390 C / 734 F is hot....I see foam at much lower temps.

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16 hours ago, uguntde said:

Chemists would use an electrical heating mantel. But this does not distribute heat evenly, nor does a sand bath. You also need a magnetic stirrer to keep temperature exposure more even.

My point was that a thick pot, or a sand bath distributes the heat much more evenly than a thin pot on an electric hot plate, where the few points where the pot is touching the heating element will get much hotter than surrounding areas. With good enough heat distribution, a stirrer doesn't seem to be needed. The volatiles escaping seem to move the liquid around enough that it colors evenly.

My "oven" provides equal heat from all sides. Again, a way of extracting the volatiles is needed so they don't build up in the oven and catch fire or explode.

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