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Varnish making - questions for the chemists


Jacob

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Hi Jacob- I'll have to make some runs that I made a long time ago with rosin, lead drier, linseed oil and thinner to work out amounts and sequence. It is a very nice varnish, but I just spread it out on glass and never applied it as a brushed coating.

Making copal varnish becomes routine once you understand the process,and made in small quantities enough to do a few inst's.

In response to Johnmasters regarding "correlation of molecules", this is way beyond my knowledge in reactions. This sudden boiling probably could be explained by careful observation of temperature during that stage. I'm way too old for that, I can hardly get up to get another beer- fred

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Jacob

 

Any luck cooking the resin long and slow for color? I have 6-7 pounds of resin to experiment with. Right now I'm preparing the HRO with the hot water, sand and salt method. My water must be very hard because I'm getting a lot of break. I'm using the Allback cold pressed Swedish linseed oil. I did my first wash today with six cups and only lost half a cup. I was expecting to lose much more.

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Ernie, I will try in in summer, it's too cold here at the moment to try and slow-cook outside for several days non-stop. I've given it some thought already, and it sounds like it should be plain colophony, not darker stuff like Burgundy resin or Strasbourg balsam. What do you think? I'll be VERY interested in your results, which should precede mine by several months.

 

BTW, the solvent question seems to get misinterpreted everytime I bring it up. My puzzlement is not whether the classical Cremomese makers used solvent or not, or what solvents were available then, but whether they had access to pure gum spirits to add during the making process, in light of the current claim by some that a resin/oil varnish cooked without gum spirits isn't a "proper" varnish. William Fulton states quite categorically in his varnish book that pure gum spirits was NOT available prior to the development of the steam distillation process around 1760. He calls the turpentine available prior to that a "crude alembic" more like the thick oxidized gum spirits which his varnish recipe requires.

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I keep hoping that question will be answered each time you ask. I will be using plain light colophony from this source...

http://www.diamondgforestproducts.com/index.html

 

I haven't  received it yet but I know their turpentine is the real stuff. I'll keep you posted once I start cooking the resin and this time I will be using an IR temp gauge and keeping notes. I bought a tall asparagus pot like Roger and others have mentioned using a pot with tall enough sides and will be using a sand bath. I also have an induction cooktop which keeps the temp very constant. I love it for glue.

 

I think the Burgundy resin is too yellow. The nicest color I got was using Larch turpentine. It turned a nice red not yellow or brown.

 

 OK Thanks Jacob.

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Jacob

 

Any luck cooking the resin long and slow for color? I have 6-7 pounds of resin to experiment with. Right now I'm preparing the HRO with the hot water, sand and salt method. My water must be very hard because I'm getting a lot of break. I'm using the Allback cold pressed Swedish linseed oil. I did my first wash today with six cups and only lost half a cup. I was expecting to lose much more.

 

Might I suggest cooking several small batches. Something often goes wrong and you don't want too much waste. You can also experiment with keeping careful records. Small batches are also much easer to deal with.

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I found on the web mention of the name "Willem Pekstok" who seems to have been an art dealer in Amsterdam in early 17th century who was already distilling turpentine to get spirit. there is a remark attributed to Rubens and Van Dick to "dipping the brush in turpentine occasionaly before blending the colours...". So I would think gum turpentine was available in Stradivarius time.

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I found on the web mention of the name "Willem Pekstok" who seems to have been an art dealer in Amsterdam in early 17th century who was already distilling turpentine to get spirit. there is a remark attributed to Rubens and Van Dick to "dipping the brush in turpentine occasionaly before blending the colours...". So I would think gum turpentine was available in Stradivarius time.

 

According to William Fulton the product of the dry distillation of pine gum is not the same as pure gum spirits which is obtained by steam distillation. In his varnish book he mentions the difficulty in determining exactly what is meant by the term "turpentine" in old manuscripts. I'm not for or against anything, I'm just trying to establish whether pure gum spirits is essential in the cooking of a pine-resin/oil varnish (added while the brew is still hot) and whether PURE GUM SPIRITS was available to the Cremonese.

 

In other words, if someone could tell use what kind and quality of turpentine is obtainable from dry distillation, when steam distillation became the common method, and how the two products differ from each other (if at all) I would be immensely grateful.

 

The Marciana recipe does not call for "turpentine". If this recipe, and other similar ones, are bound to fail because of this, surely by now it would have been evident and common knowledge?

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Well if you consider that dry distillation does not lead to pure spirit turpentine then you have to conclude that pure spirit turpentine is not absolutely necessary to make a good oil varnish since the Cremonese varnish is said to be very good while only dry distillation was available (assuming it's really the case)

... ;)

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this link for example implies that steam distillation was used way before the 17th century. But steam distillation seems to be used when people know they are dealing with heat sensitive material. Was there any hint that turpentine was better when it was made by steam distillation? there is a drawing of Pekstok distillation apparatus but I couldn't find it.

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Actually in reading the text (national gallery technical bulletin bulletin, 1994) about Pekstok here is what it is said "

On a larger scale, as would be needed for painting purposes, the oil was distilled by heating the crude gum turpentine in a large copper kettle: Fig. 9 shows the apparatus used by Willem Pekstok in Amsterdam, who distilled turpentine from 1658. Great care appears to have been taken to regulate the temperature of the distillation, using a gentle heat and adding water to the gum resin so that the turpentine oil distilled over at a lower temperature; cold water was also used as a coolant for the collecting vat. The process was monitored by testing the resin at intervals. Ninety pounds of turpentine oil and 470 pounds of residual colophony were obtained from 570 pounds of starting material (note 72). De Mayerne recommended that the solvent be redistilled before use (note 73). Lavender, or spike, oil had slightly different solvent properties - it would, according to Pomet, dissolve sandarac resin -but its recommended uses in painting were similar to those of turpentine (note 74)."

 

So in essence it would be steam distillation.

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Actually in reading the text (national gallery technical bulletin bulletin, 1994) about Pekstok here is what it is said "

On a larger scale, as would be needed for painting purposes, the oil was distilled by heating the crude gum turpentine in a large copper kettle: Fig. 9 shows the apparatus used by Willem Pekstok in Amsterdam, who distilled turpentine from 1658. Great care appears to have been taken to regulate the temperature of the distillation, using a gentle heat and adding water to the gum resin so that the turpentine oil distilled over at a lower temperature; cold water was also used as a coolant for the collecting vat. The process was monitored by testing the resin at intervals. Ninety pounds of turpentine oil and 470 pounds of residual colophony were obtained from 570 pounds of starting material (note 72). De Mayerne recommended that the solvent be redistilled before use (note 73). Lavender, or spike, oil had slightly different solvent properties - it would, according to Pomet, dissolve sandarac resin -but its recommended uses in painting were similar to those of turpentine (note 74)."

 

So in essence it would be steam distillation.

 

Thanks, that's very helpful.

 

However, even if we assume that this product was already availailable during the late 1500's/1600's in Cremona, we can't be sure it was used as a CONSTITUENT part of their varnish. That is, not if they made their oil varnish in a similar way as the Marciana recipe describes. I'm wondering if mastic is prescribed in the Marciana recipe to aid drying - I remember the phrase "mastic is a ferocious dryer" cropping up in the distant past on this forum.

 

Roger Hargrave and others don't use turpentine as solvent during preparation, nor as a thinner afterwards. So, there are different practices and theories of which I'm trying to make sense. What makes practical sense to me is a varnish which doesn't require a solvent or thinner, can be applied in a few thick coats, dries easily, and doesn't need coloring matter added.

 

Which recalls the findings of Eckhard: the varnish consists of pine resin, linseed oil and mastic.

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I agree. And for example I made a varnish only with larch turpentine that I cooked at

 about 100-110C until most volatile constituants were gone ( well, at least as judged by steam/smoke coming out) and linseed oil (because these were found by Echard). the result is a thick honey like varnish that you can apply with fingers or with a brush if I add some white spirit. Of course I don't have much experience and I don't know how it will behave with time.

the other thing is that we don't know if Stradivarius and the others were actually making their varnish. Maybe they were just buying it, adding some pigments, adding some turpentine to make it thinner or maybe not.

I don't remember Echard finding mastic in it, but for example it's not unthinkable that varnish makers were working in factories where different kinds of varnishes were made with different resins so that today's analytical methods could find traces of resins that were actually not used in Stradivarius varnish but simply ended up there the same way "traces of nuts" appear in food you can buy today even though the food "doesn't contain nut"... :)

 

.

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Who's claiming this, Jacob?

Sorry if I've missed something obvious....

Roberdo...#51

But it is still possible to make varnish without adding turpentine during or after cooking. Whether it is a good varnish in the long run is another story of course.

 

Ernie...#52

Why would solvent free varnish not be good. Koen Padding and Donald Fels varnishes do not contain solvents and they are well respected varnish makers.     

 

John

It may be my post to Robert...Sorry Robert I wasn't picking on you. I plan on making some solvent free varnish and I know others make it as well.

 

-Ernie    

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Roberdo...#51

But it is still possible to make varnish without adding turpentine during or after cooking. Whether it is a good varnish in the long run is another story of course.

 

Ernie...#52

Why would solvent free varnish not be good. Koen Padding and Donald Fels varnishes do not contain solvents and they are well respected varnish makers.     

 

John

It may be my post to Robert...Sorry Robert I wasn't picking on you. I plan on making some solvent free varnish and I know others make it as well.

 

-Ernie    

Don't be sorry Ernie... :)

What I meant to say of course was that I had not enough experience with varnish so that I could not talk about the effect of time on "spirit of turpentineless" varnish.

.

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Who's claiming this, Jacob?

Sorry if I've missed something obvious....

 

Hi John,

I think that the reference is to me.  It is not that I do not think that resin and oil melted together is not a good finish.  Quite the contrary.  However it is not [in varnish making terms] a varnish.  It is a bodied oil which has very different properties...most important...it does not have the film forming characteristics of a varnish.  Personally, the earliest instrument I have had at close examination...that shows this kind of varnish film...is a 1582 deSalo viola.  Seems to me that the violin world latched on to turpentine in the varnish quite early.

Joe

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Hi John,

..it does not have the film forming characteristics of a varnish.  

Hi Joe, at the risk of me sounding like a complete buffoon, what does this mean, and how can you tell if a varnish has it or not?

I have to say that the Marciana-type stuff forms a perfectly good film according to my everyday understanding of the term, but I guess you have something more technical in mind?

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If I may add to this query - Joe, unless I misunderstand you, you can SEE whether a classical varnish contains turpentine or not - and therefore that the classical Cremonese instruments contain turpentine in the varnish. To me this poses a profound question - would someone like Roger Hargrave have spent all the time and effort on developing a concoction which isn't really "varnish" when his aim, unless I seriously misunderstood him, was to emulate a Cremonese finish?

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Jacob, on 25 Jun 2013 - 11:14 PM, said:

Ernie, I will try in in summer, it's too cold here at the moment to try and slow-cook outside for several days non-stop.

you can cook it over several "sessions", it doesn't have to be non-stop.

Jacob, would an electric crockpot not be hot enough?

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Jacob, on 25 Jun 2013 - 11:14 PM, said:

Ernie, I will try in in summer, it's too cold here at the moment to try and slow-cook outside for several days non-stop.

you can cook it over several "sessions", it doesn't have to be non-stop.

Jacob, would an electric crockpot not be hot enough?

 

Don, my apologies - but what is a crockpot? A picture will help. I guess I can google it myself.

 

Anyhow, the earlier suggestion that I could do it in stages was helpful. I don't have any colophony in stock right now, but I need to put in an order with Kremer, so perhaps I'll start giving this a go in about a month's time.

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