Varnish making... and Lake making

[MikeC]

There's an infinity of varnish threads on the forum so naturally I'll start another one.  

Yesterday I tried making varnish.   Thoughts,  comments, suggestions anyone?  

 I was basically following the procedure shown in this link,   https://www.ruschil.com/blog/making-violin-varnish

using 6 oz.  of linseed oil and 6 oz.  of pre cooked rosin.   The cooking lasted about 2 hours but I was using a cheap electric hot plate and it was hard to maintain a steady temperature.  I tried to maintain 350f    At the end of the cook at a lower temp (100c)  I added in 0.6 oz.  of mastic.  

It never did pass the 'string test'.  Did I not cook it hot enough or long enough?    I brushed a little of it on a scrap of maple last night and this morning it seems to have sunk into the wood leaving only an oily film on the surface.    That was last night so it has not had any UV exposure yet, it will get some sun today.  

In the attached photo,  the right side is the varnish.  For comparison with some previous experiments, the thin strip on the far left is a previous cold mix of oil / rosin / turpentine and the thin strip in the middle is rosin dissolved in alcohol.  Notice how those two leave a shiny surface layer compared to the varnish I made yesterday.   

I think today I'm going to put some of it in a small babyfood jar and bring it up to a higher temp and see what effect that has on it.   

Any advise from you varnish experts would be welcomed! 

 

 

 

[jefcostello]

The point of string testing is that it is meaningless....

The test that means the most to me is Don's fingerprint test: press your hand against the varnish for more than 15 seconds without any fingerprints.

If you like strings, you can use more resin or boil the resin harder...

It’s supposed to be shiny.

[Brian in Texas]

You mention the varnish soaking into the wood. Did the scrap have a ground sealer on it, or was it just bare wood when the varnish was applied?

[Davide Sora]

Have you tried a drop on the glass to see if the mixture is homogeneous or if there is some sort of separation between the components? This could indicate incorrect cooking.

Another drop spread thinly on the glass gives you some indication of the drying. Wood introduces the variable of absorption that could confuse things regarding the basic quality of the varnish. Glass also allows for a better evaluation of the actual transparency.

[LCF]

Any sealer on that wood? I'd guess that the shinier blobs were probably more viscous. Viscosity is the main thing that stringing tells you, dryability not so much. 

I made a batch of really very long and slowly cooked oil then added resin and cooked it for another aeon. No thinner added. When I poured it into a bottle and it cooled down it was so viscous that if I tipped the bottle upside down it took a couple of bulbous minutes to flow downwards. When thinned it did not set.

[Steve Voigt]

You're right, there are a lot of varnish threads, so I'll stick to the specifics…

1. The number one factor in getting this varnish to string is how you pre-process your oil. Number two is pre-processing the rosin, but it sounds like you took care of that. If you wash your oil, and then cook it, something like 450-500 F for 30-60 minutes, it should combine with resin and produce a nice string almost immediately.  (only cook the oil at the high temp after first getting rid of ALL water at a lower temp!) The lower temp mentioned in the recipe will get rid of water, but may not pre-polymerize the oil enough to get a good string.

2. Depending on how you cooked your rosin, 350 F may not be hot enough. Your recipe specifies a week at 350, but doesn't mention whether the lid is on or off, or how much weight loss there is. If you had the lid off, the melting point point of the resulting resin may be high enough that 350 F will not allow you to combine the resin and oil sufficiently. 

3. I will second @Davide Sora 's recommendation for testing on glass. Put a drop on glass. Tip the glass vertically so the varnish runs and forms a bead. Observe hardness, gloss, and drying time. You will learn a lot.

Good luck!

[MikeC]

I pre cooked the oil after washing it,  I don't remember what temperature but had it on the heat for a couple hours.

There was no sealer on the maple sample.   Viscosity of the varnish is about like room temperature honey, maybe a little less viscous than that.    

I'll  try some on a piece of glass as suggested, or a ceramic plate and see what happens.   The other two samples that I mentioned that are glossy and stay on the surface are both quite thin.  

More later,  I have some errands to run...  

[M Alpert]

Excellent advice from @Steve Voigt 

In addition I would add that in my experience the magic happens between 250-280°C. Considerably hotter than what you cooked...

[Davide Sora]

30 minutes ago, MikeC said:

I'll  try some on a piece of glass as suggested, or a ceramic plate and see what happens.  

For me, clear glass not too thick is better than ceramic because you can observe against the light by looking with a lens, evaluating the true transparency and if there is something strange with the amalgam.

[Davide Sora]

36 minutes ago, MikeC said:

I pre cooked the oil after washing it,  I don't remember what temperature but had it on the heat for a couple hours.

I would also do the drop test on glass with the oil alone to be sure its drying properties and transparency are correct (it should dry to a transparent layer) to rule it out in case of subsequent problems.

[MikeC]

After an afternoon in the sun yesterday... 

I don't have a piece of glass but I put some on a white ceramic plate.  In a thin layer it's dry to the touch but still takes a fingerprint.  

Similar results on sealed wood..  

Is it ok to put it back on the heat and cook at a higher temp?    I may try that with a small sample.    I could put some in a babyfood jar in a sand bath and heat it up and see what happens.   

[MikeC]

I kinda got the impression that I didn't cook it hot enough.  So today I put some in a jar in a sand bath and cooked it some more.  It held a fairly steady temperature of about 460f.  I decided to thin it some with turpentine,  may have used too much, I'm not sure.   I could warm it up and let some of it evaporate.    Anyway,  I'll do some test samples tomorrow.  

 

[LCF]

1 hour ago, MikeC said:

I kinda got the impression that I didn't cook it hot enough.  So today I put some in a jar in a sand bath and cooked it some more.  It held a fairly steady temperature of about 460f.  I decided to thin it some with turpentine,  may have used too much, I'm not sure.   I could warm it up and let some of it evaporate.    Anyway,  I'll do some test samples tomorrow.  

 

 

Is that 460 in the jar or the sand or the electric elephant?

 

Watch your eyebrows. How's the smoke?

[MikeC]

1 hour ago, LCF said:

Is that 460 in the jar or the sand or the electric elephant?

 

Watch your eyebrows. How's the smoke?

Laser thermometer pointed straight down at the varnish,  not sure how accurate it is.    I have a faceshield and made sure I was upwind of the neighbor that I don't like.     

[M Alpert]

6 hours ago, MikeC said:

Laser thermometer pointed straight down at the varnish,  not sure how accurate it is.    I have a faceshield and made sure I was upwind of the neighbor that I don't like.     

My experience:

With any smoke or fumes a laser thermometer reading is unreliable. I prefer to use a metal stick thermometer as well, although it's hard to find these to go up to 250 C.

I have used exactly this setup, baby food jar and sand, with small amounts it works well but the temperature is rarely homogeneous throughout, meaning stir often.

Again, in my experience, the magic starts around 250 C. Above 280 and you will burn the stuff.

[M Alpert]

Another note, I would not heat it up to this temperature with any amount of turpentine in it, for fear of combustion. Apparently lamp oil can be used as a thinner, and reheated up to these temperatures, according to Pierre flavetta. I haven't tried that yet.

[uguntde]

On 4/4/2025 at 3:41 PM, Davide Sora said:

Have you tried a drop on the glass to see if the mixture is homogeneous or if there is some sort of separation between the components? This could indicate incorrect cooking.

Another drop spread thinly on the glass gives you some indication of the drying. Wood introduces the variable of absorption that could confuse things regarding the basic quality of the varnish. Glass also allows for a better evaluation of the actual transparency.

EVen if you don't fuse it the rosin components (abietic acid) will dissolve in the oily components.

[uguntde]

7 hours ago, MikeC said:

Laser thermometer pointed straight down at the varnish,  not sure how accurate it is.    I have a faceshield and made sure I was upwind of the neighbor that I don't like.     

Infrared thermomters (the laser tells you just where you measure) should work perfectly well. They fail in electromagnetic fields - to be sure switch off the cooked shortly before you measure.

I recommend to buy a laboratory cooker / magnetic stirrer - they are available with a temperature control. This kind of thing:

https://www.carlroth.com/de/en/magnetic-stirrer-with-hotplate/heating-magnetic-stirrers-rotilabo-mh-20-digital-set-with-integrated-contact-thermometer/p/eye7.1

Even better: A heating mantle: https://www.carlroth.com/en/en/heating-mantles-heating-lines/heating-mantle-pilz-whlg-classic-series-model-whlg2---heat-zone-switch/p/ke91.1

The danger of something exploding can me managed much better in such a setup. You can add a stopper that turns away and lets you control how much you evaporate.

 

[MikeC]

In the original link, the recipe called for 1 to 2 percent siccative.   I don't have any and didn't use any.   Would it be a good idea to add a little japan drier?   

[Davide Sora]

48 minutes ago, uguntde said:

EVen if you don't fuse it the rosin components (abietic acid) will dissolve in the oily components.

Interesting, so some questions arise:

How long does it take for rosin to dissolve in oil in a cold mix? 

Once dissolved, is it a homogeneous and crystal clear solution? 

Are you talking about untreated (and therefore more acidic) rosin, cooked rosin, or limed rosin?
Or raw resin (tree exudate), which also contains turpentine?

Do you think cold dissolution could be enough to make a good oil varnish? It would be great to avoid all those annoying and dangerous cooking.

[LCF]

1 hour ago, M Alpert said:

My experience:

With any smoke or fumes a laser thermometer reading is unreliable. I prefer to use a metal stick thermometer as well, although it's hard to find these to go up to 250 C.

 

Not only with smoke and fumes. Infrared thermometers give wildly varying results depending on the emissivity of the item being measured  ag aluminium typically gives a low reading. Although you can calibrate them for specific surfaces. 

I used to use a high temp glass thermometer for varnish then I switched to using a k type thermocouple  with a suitable multimeter but using the thermocouple to control the heating element by the use of cheap PID controller is the best solution.

 

[MikeC]

2 hours ago, Davide Sora said:

Interesting, so some questions arise:

How long does it take for rosin to dissolve in oil in a cold mix? 

Once dissolved, is it a homogeneous and crystal clear solution? 

Are you talking about untreated (and therefore more acidic) rosin, cooked rosin, or limed rosin?
Or raw resin (tree exudate), which also contains turpentine?

Do you think cold dissolution could be enough to make a good oil varnish? It would be great to avoid all those annoying and dangerous cooking.

HI Davide,   I mixed up an uncooked varnish and I think it works well.    I used the cooked rosin,  cooked at 350f for about 3 hours.   I first dissolved the rosin in turpentine and then added an amount of linseed oil equal to the rosin amount.  As I recall I think it was by weight not volume.   See the left strip of varnish on my test sample shown here, the narrow strip near my thumb.  It dried well, looks transparent.  I don't know how it would work long term.   

[Davide Sora]

1 hour ago, MikeC said:

HI Davide,   I mixed up an uncooked varnish and I think it works well.    I used the cooked rosin,  cooked at 350f for about 3 hours.   I first dissolved the rosin in turpentine and then added an amount of linseed oil equal to the rosin amount.  As I recall I think it was by weight not volume.   See the left strip of varnish on my test sample shown here, the narrow strip near my thumb.  It dried well, looks transparent.  I don't know how it would work long term.   

Yes, I also made a cold mix short-oil varnish by first dissolving the rosin in turpentine. Used only a few times as a ground, as a real varnish it was too fragile. The main point with any oil varnish is knowing how it behaves in terms of wear, chippiness, craquelures, etc. in the long term, which is always the missing information.

[DenisR]

On 4/4/2025 at 2:12 PM, MikeC said:

 I was basically following the procedure shown in this link,   https://www.ruschil.com/blog/making-violin-varnish

Thank you for this new thread.

I came across this page, which is both beautiful and detailed. However, when I read that the rosin needs to cook continuously for a whole week, I gave up on the idea of trying it.

How do you manage such long cooking times? Even in the garden, I wouldn’t feel comfortable leaving it to cook overnight without anyone keeping an eye on it.

Alternatively, could I cook it for a few hours each day, let it cool overnight, and then reheat it the next morning?

Wishing you a great start to the week!

[MikeC]

3 hours ago, DenisR said:

Thank you for this new thread.

I came across this page, which is both beautiful and detailed. However, when I read that the rosin needs to cook continuously for a whole week, I gave up on the idea of trying it.

How do you manage such long cooking times? Even in the garden, I wouldn’t feel comfortable leaving it to cook overnight without anyone keeping an eye on it.

Alternatively, could I cook it for a few hours each day, let it cool overnight, and then reheat it the next morning?

Wishing you a great start to the week!

HI Dennis,    The article says to cook for a week for the color of the varnish.  For an uncolored varnish you don't have to cook that long.   I cooked the rosin for about 3 hours at 350f.  

The article also says to use an unspecified siccative.  I ordered some japan drier from amazon and hopefully that will make the varnish dry better.  

I wouldn't leave it unattended either.  If I wanted a week long cook,  I would heat it for a few hours, let it cool,  then heat it again when I can be there to watch it.    Don't let it cool off in the pan though because when you start heating it back up again it might burn on the bottom before it all melts.    Instead,  pour it out into a baking sheet lined with aluminum foil and let it cool.   When you are ready to start heating it again, break it into pieces and put it in the pan.   It doesn't stick to the aluminum foil.   

 

This is what it looked like after I broke it into pieces from the baking sheet.