Varnish Making - Use of Manganese

[David Stiles]

Hi, please forgive me for starting yet another varnish making thread.   I have been resisting but after reading everything that I can find here, I am still confused.   

My recent batch of oil varnish based on Rodger Hargraves' recipe has been reasonably successful however there is room for improvement in relation to drying time in my humid climate.   

I have experimented with Allback Manganese Drier and it does assist drying.  It is very concentrated; I used it at the rate of 1 drop in 5 grams of varnish which may be very strong; hard to know.   I have also tried Sennelier Cobalt Drier at 2% but I could not detect any improvement in drying.   Not sure if I want to be adding driers.

For my next batch, I have been looking at Jackson's recipe posted in another thread that includes a small amount of Calcium hydroxide as well as Manganese oxide.  I understand that the manganese is there to improve the partial solubility of caused by the Calcium.  At about 0.25% is the manganese is enough to be acting as a dryer also?

https://maestronet.com/forum/index.php?/topic/351665-violin-varnish-products-in-australia/&do=findComment&comment=966793   

Another option is cooking in Burnt Umber.  Although there are widely differing opinions,  it is used by some to colour the varnish and to improve drying.  I have some Burnt Umber dry pigment which I mulled into a small quantity of varnish to look at the colour and it appears to have slowed down the drying process.  I remember reading that too much dryer can do this.  If Burnt Umber is to be cooked in, how much is too much?

 

 

 

[Michael Szyper]

5 hours ago, David Stiles said:

Hi, please forgive me for starting yet another varnish making thread.   I have been resisting but after reading everything that I can find here, I am still confused.   

My recent batch of oil varnish based on Rodger Hargraves' recipe has been reasonably successful however there is room for improvement in relation to drying time in my humid climate.   

I have experimented with Allback Manganese Drier and it does assist drying.  It is very concentrated; I used it at the rate of 1 drop in 5 grams of varnish which may be very strong; hard to know.   I have also tried Sennelier Cobalt Drier at 2% but I could not detect any improvement in drying.   Not sure if I want to be adding driers.

For my next batch, I have been looking at Jackson's recipe posted in another thread that includes a small amount of Calcium hydroxide as well as Manganese oxide.  I understand that the manganese is there to improve the partial solubility of caused by the Calcium.  At about 0.25% is the manganese is enough to be acting as a dryer also?

https://maestronet.com/forum/index.php?/topic/351665-violin-varnish-products-in-australia/&do=findComment&comment=966793   

Another option is cooking in Burnt Umber.  Although there are widely differing opinions,  it is used by some to colour the varnish and to improve drying.  I have some Burnt Umber dry pigment which I mulled into a small quantity of varnish to look at the colour and it appears to have slowed down the drying process.  I remember reading that too much dryer can do this.  If Burnt Umber is to be cooked in, how much is too much?

 

 

 

A spoon of caoh and 5% per weight of alum, heated to 280C for 1-2 Minutes will do the job without being toxic as manganese. It makes the varnish more alcohol soluble and a bit softer (less chippier), so you might adjust the resin ratio for antiquing.

[FiddleDoug]

I'm hardly an expert on this, but I'll just pass on my very limited experience. I was using a commercial varnish, and adding transparent iron oxides for color. It worked really well during application, but if I had any left over, it gelled within a couple of hours. Umber is a natural pigment that contains manganese oxide, and iron oxide. I would think that if you tried to cook it in, it might gel up immediately.

[ctanzio]

I believe Burnt Umber contains Manganese, but it also contains other materials that can have negative effects on the drying time and mechanical properties of the film.  For example, old oil paintings that used burnt umber can develop a discolored sheen or nodule-like bumps.

These effects can vary dramatically among various producers of the Burnt Umber so the rule is experiment with the product of various suppliers to see what works.

Because there is variation in the chemical makeup among the suppliers of linseed oil and one's preparation of the oil, the amount of drier to be added to the oil is a bit of a guess, but over the years there have been some "rules" that seem to work "good enough".

By weight, 0.1% metal to oil, or 0.5% of drying compound to oil.

Szyper's 5% recommendation for Alum is still in the ballpark because Aluminum is about half the weight of the more common driers and the overall chemical composition, I think, is heavier than the oxides of Cobalt, Manganese and lead, so more alum is needed to get a decent concentration of Aluminum ions to catalyze drying.

Something to keep in mind is that the use of metal driers also results in the increased production of volatile compounds that want to migrate to the surface of the film and evaporate. Humid environments, or a UV box with no ventilation, might give rise to unwanted effects.

An easy way to determine the drying effects of various concentrations of compounds is by measuring the weight gain of the film over time. For example, get a small glass plate and weight it. Now cover it with a coat of linseed oil and weight it again. Every 4 to 12 hours or so over the next 7 days reweigh the plate and notice the increase.

It may take a day or so before you notice a significant increase in weight. This is called the "induction period" of the drying. The weight should continue to increase dramatically until about day 5 or so then start to level out. Over the next few weeks it should peak and start to slowly decrease.

Now repeat the experiment for the same linseed oil brand but with a measured amount of drier added. Start at say 0.1% by weight (0.001x the weight of the linseed oil used.)

You should notice the induction time, the time to start rapidly increase in weight, shorten. At some concentration of drier by weight, there will be no more effect on the induction time or the time when the weight gain starts to level off. That is, more or less, the ideal concentration of drier.

Since you cook your oil, you may have to perform the experiment using that process. For example, do you add the drier before or after you cook the oil?

The weight increase represents the absorption of oxygen from the air as the linseed oil compounds combine into long chains. Driers accelerate this process, but the combination reactions with and without the drier are somewhat different so the finished hardened surface is not exactly comparing apples to apples so to speak. There are some long term differences (like 10+ years) that can occur.

 

[violins88]

I presume the weight gain is because of oxidation. Is that right?

[JacksonMaberry]

24 minutes ago, violins88 said:

I presume the weight gain is because of oxidation. Is that right?

Yes, the absorption of oxygen is what causes the oil film to cure and increase in weight. 

[John Harte]

There are excellent comments above.  What follows here is, at best, bucket chemistry and an example of how one probably shouldn't do things....

Around 12 years ago I made up batches of various varnishes with various additives cooked into the oil component.  One involved cooking 5% by weight Burnt Umber (Kremer 4070, now listed as 40700) into Langridge Cold Pressed Linseed Oil.  According to my notes this mixture was heated up to 260ºC following which it was combined with an equal weight of pre-cooked pine resin.  This varnish has always dried reasonably, it being capable of eventually doing so even without the need to use sunlight or UV drying cabinet.  Over the past 12 years it has been used in many and varied samples.  Other than very slight surface wrinkling in a few very thickly applied single applications, I don't recall any issues.  Mind you, 12 years is not long in the scheme of these things.  This varnish has continued to thicken in the bottle over time but the addition of further oil of turpentine has so far always worked in getting it back into a workable state.

Over the last 2 or 3 years I have been adding James C. Groves Siccative de Courtrai to various varnish samples.  This has been for several reasons, the main one being wanting varnishes without cooked in siccatives that would dry without the need to use sunlight or UV cabinet.  Groves mentioned in an email that I might start by trying 10 drops per oz. of varnish but thus far I've been far too sloppy to bother measuring anything accurately.  I'm not sure that I would use it when varnishing an instrument but so far so good in terms of the various samples where it has been used...

[David Stiles]

Thank you everyone for your comments.   

@ctanzio very helpful explanation of what's going on.  It is difficult to determine metal content in commercial products so, as you point out, testing is important.  

 

On 3/15/2023 at 4:20 PM, Michael Szyper said:

A spoon of caoh and 5% per weight of alum, heated to 280C for 1-2 Minutes

'Spoon' is a vague term, is quantity not critical?    Are we cooking the compounds with the oil, resin or after mixing?

On 3/16/2023 at 2:59 PM, John Harte said:

One involved cooking 5% by weight Burnt Umber (Kremer 4070, now listed as 40700) into Langridge Cold Pressed Linseed Oil.  According to my notes this mixture was heated up to 260ºC following which it was combined with an equal weight of pre-cooked pine resin.

5% seems a lot.  Is it enough to colour the varnish significantly?   Is it usual to cook in oil before resins are added?

 

On 3/16/2023 at 2:59 PM, John Harte said:

This varnish has continued to thicken in the bottle over time

This raises the question of how much shelf life is affected by cooked in driers?

 

[Michael Szyper]

3 minutes ago, David Stiles said:

Spoon' is a vague term, is quantity not critical?    Are we cooking the compounds with the oil, resin or after mixing?

It isn’t critical. Just need to understand what it makes with your varnish - the more you add the less acidity with increasing resin hardness due to resin and oil soaps forming. You can add the lime to each of the or to the varnish. You don’t have to lime at all. 

[JacksonMaberry]

I'm with Michael. While I do make a habit of conducting things very carefully/repeatably when making synthetic resins, the actual cooking is more an art than a science. Lime the resin or don't, use some umber or not, and just a spoonful or a pea sized ball or x% by mass. Whatever you do, write it down and consult it later.

I'd not lime the oil, personally, and I still think liquid process rosinates are to be preferred, but I won't bang that drum further.

[joerobson]

In my not so humble opinion: A well formed varnish should not need a siccative.  Does your varnish dry @ one coat per day?

If not you might look closely at oil preparation.  A well processed oil will make a varnish that dries through the film.  Non lead driers tend to dry top down and not through the film.  This opens up the possibility of other problems as the film ages.

on we go,

Joe

[JacksonMaberry]

2 hours ago, joerobson said:

In my not so humble opinion: A well formed varnish should not need a siccative.  Does your varnish dry @ one coat per day?

If not you might look closely at oil preparation.  A well processed oil will make a varnish that dries through the film.  Non lead driers tend to dry top down and not through the film.  This opens up the possibility of other problems as the film ages.

on we go,

Joe

Seconded. Oil prep is the most critical part of the game. 

[John Harte]

15 hours ago, David Stiles said:

5% seems a lot.  Is it enough to colour the varnish significantly?   Is it usual to cook in oil before resins are added?

This raises the question of how much shelf life is affected by cooked in driers?

Yes 5% may seem a lot.  However, according to my reading, burnt umber is typically made up of 5 to 20% manganese oxides and hydroxides and a larger percentage of iron oxides.  As such, in the oil component of the varnish, manganese oxide and hydroxide presence would likely be no higher than 1%.  As for the iron component, that probably does contribute to the colour but I would not consider the particular varnish that I have mentioned to be particularly dark, not appreciably more so than equivalent varnishes without cooked in additives.  Other factors like the cooked resins involved and their treatment etc., seem to influence colour outcomes more than the addition of the burnt umber that I mention has.

I should mention that not all Burnt Umbers are equal.  I have tried others and the outcomes were not as good...

My understanding is that siccatives are cooked into the oil before resins are added.  This is what I have done.  I have tried burnt umber mulled into varnish but wasn't convinced by the outcome.

Re your mention of shelf life, my impression based on experience is that cooked in driers do generally accelerate thickening.  If they don't, then whatever you have added is probably not functioning overly well as a drier.  Everything is relative.  All oil varnishes will thicken to a greater or lesser extent depending any number of factors.  Various storage conditions can be employed that will help limit thickening to at least some extent.

[John Harte]

8 hours ago, joerobson said:

In my not so humble opinion: A well formed varnish should not need a siccative.  Does your varnish dry @ one coat per day?

If not you might look closely at oil preparation.  A well processed oil will make a varnish that dries through the film.  Non lead driers tend to dry top down and not through the film.  This opens up the possibility of other problems as the film ages.

on we go,

Joe

Does your mention of drying @ one coat per day include the need for some form of UV?

I agree with what you mention re surface driers.  If manganese was to be used, I would be inclined to combine it with a through drier.

[joerobson]

1 hour ago, John Harte said:

Does your mention of drying @ one coat per day include the need for some form of UV?

I agree with what you mention re surface driers.  If manganese was to be used, I would be inclined to combine it with a through drier.

John,

Yes...UV black.light about 8" from the surface.

Joe

[David Stiles]

 

 

How do we define dry in this case?  not sticky? or no fingerprinting? 

[David Stiles]

13 hours ago, joerobson said:

Does your varnish dry @ one coat per day?

How do we define 'dry' in this case?  not sticky? or no fingerprinting? 

[Michael Szyper]

19 hours ago, joerobson said:

In my not so humble opinion: A well formed varnish should not need a siccative.  Does your varnish dry @ one coat per day?

If not you might look closely at oil preparation.  A well processed oil will make a varnish that dries through the film.  Non lead driers tend to dry top down and not through the film.  This opens up the possibility of other problems as the film ages.

on we go,

Joe

Having fought with plenty of varnish issues, drying was never a problem, even if i used the worst quality and didn’t „prepare“ it at all. But this might be also due to the rather lean varnishes i make, where oil quality isn’t that important in terms of drying time.

[joerobson]

7 hours ago, David Stiles said:

How do we define 'dry' in this case?  not sticky? or no fingerprinting? 

Solid through the film just applied.

[joerobson]

28 minutes ago, Michael Szyper said:

Having fought with plenty of varnish issues, drying was never a problem, even if i used the worst quality and didn’t „prepare“ it at all. But this might be also due to the rather lean varnishes i make, where oil quality isn’t that important in terms of drying time.

True.

[David Stiles]

2 minutes ago, joerobson said:

Solid through the film just applied

Thanks Joe. 

I'm probably not getting 'solid through film' dry in 24hrs.   One issue might be film thickness.  I am applying varnish as thin as I can with fingers but it does have the viscosity of honey, so may be film is too thick. 

I recently did a test on a plastic and found that 6 coats was 90 microns thick.  That's 15 microns  per coat.  How does that sound? 

 

 

[joerobson]

5 hours ago, David Stiles said:

Thanks Joe. 

I'm probably not getting 'solid through film' dry in 24hrs.   One issue might be film thickness.  I am applying varnish as thin as I can with fingers but it does have the viscosity of honey, so may be film is too thick. 

I recently did a test on a plastic and found that 6 coats was 90 microns thick.  That's 15 microns  per coat.  How does that sound? 

 

Ĺ

I must admit that I have never made these measurements.

[JacksonMaberry]

90 microns is a pretty thick finished film, and if that's in only 6 coats I'd want to see thinner coats personally. I'm getting 5-7 microns per coat, and get to the finish line in max 7 coats. 

[John Harte]

21 hours ago, joerobson said:

John,

Yes...UV black.light about 8" from the surface.

Joe

Joe, thanks for confirming this.

John

[David Stiles]

4 hours ago, JacksonMaberry said:

90 microns is a pretty thick finished film, and if that's in only 6 coats I'd want to see thinner coats personally. I'm getting 5-7 microns per coat, and get to the finish line in max 7 coats. 

Thanks Jackson, that really does explain why I have been having trouble with drying.   I'm really happy to have got to this point.