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joerobson
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10 hours ago, Melvin Goldsmith said:

What kind of varnish are we trying to make?....A boat varnish?

If you wish to replicate the incredibly fragile and delicate nature of the Old Italian varnishes you must embrace the natural falabilty of the ingredients you consider

 

13 minutes ago, Michael Szyper said:

dito

It seems the popular method now is to cook the resins for a very long time, in order to achieve a desired colour without added pigments. With an electric hotplate, IR thermometer, good vessel, this is a successful and controllable method.

But in the 17th and 18th century, I can't see how it would have been possible, or perhaps even safe, to cook resins for hundreds of hours on open fires. Are there any historical documents which support cooking resins for these extended periods, or is this purely a modern pursuit?

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34 minutes ago, Wood Butcher said:

 

It seems the popular method now is to cook the resins for a very long time, in order to achieve a desired colour without added pigments. With an electric hotplate, IR thermometer, good vessel, this is a successful and controllable method.

But in the 17th and 18th century, I can't see how it would have been possible, or perhaps even safe, to cook resins for hundreds of hours on open fires. Are there any historical documents which support cooking resins for these extended periods, or is this purely a modern pursuit?

I don't know, the only example that comes to mind is the cooking of pitch for caulking boats and ships, where huge quantities of resin (a ship must have needed a lot of it) were cooked for many days in a row in large pots of iron until it turned black (very dark). 

So maybe boat varnish might make some sense...:D

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1 hour ago, Michael Szyper said:

By washing oil you remove phospholipids. 

This is also my understanding.

At least the hydrophilic part of phospholipids. 

I agree on the cooking.

In my experience, washing the oil also does a noticeable difference concerning stickiness of the varnish film. 

Many friends have also noticed a difference. 

 

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59 minutes ago, Wood Butcher said:

 

But in the 17th and 18th century, I can't see how it would have been possible, or perhaps even safe, to cook resins for hundreds of hours on open fires. Are there any historical documents which support cooking resins for these extended periods, or is this purely a modern pursuit?

Perhaps this type of devices might have helped for long period cooking at relatively constant temperatures the vessel was surely placed in sand. But it would need several persons taking turns, paying attention during hours and even days and nights. 

Anyway there is no easy answer. 

Fourneau-Alchimiste.jpg

ob_4570ec_glauber-03-c.jpg

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1 hour ago, Wood Butcher said:

 

It seems the popular method now is to cook the resins for a very long time, in order to achieve a desired colour without added pigments. With an electric hotplate, IR thermometer, good vessel, this is a successful and controllable method.

But in the 17th and 18th century, I can't see how it would have been possible, or perhaps even safe, to cook resins for hundreds of hours on open fires. Are there any historical documents which support cooking resins for these extended periods, or is this purely a modern pursuit?

I just took a look in Bonnani's book from 1723.

here is one of the receipt of the italian varnish  : take 8 part of Turpentine, put on fire till it reduce to 1 part....

The current usage is not so far.

Bonanni Italian varnish.JPG

Note : no (washed or not washed) linseed oil in this receipt.

then old evidence of cooking the resin at high temperature could be inside this book (1693) : https://www.amazon.com/Collectanea-Chymica-Leydensia-Maetsiana-Margraviana/dp/1166677524

while it is decribed as a text in Latin it is actually in german.

https://play.google.com/books/reader?id=Lbc5AAAAcAAJ&pg=GBS.PP6&hl=f

I will try to find the corresponding extract. 

 

 

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1 hour ago, Wood Butcher said:

 

It seems the popular method now is to cook the resins for a very long time, in order to achieve a desired colour without added pigments. With an electric hotplate, IR thermometer, good vessel, this is a successful and controllable method.

But in the 17th and 18th century, I can't see how it would have been possible, or perhaps even safe, to cook resins for hundreds of hours on open fires. Are there any historical documents which support cooking resins for these extended periods, or is this purely a modern pursuit?

To get a completely black resin which looks reddish/brown in a thin layer I need 50-70 minutes. Just a bit intuition needed in order to not burn the resin.

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@Michael Szyper , I guess you also know that the washed raw oil must also then be heat treated before being cooked in a varnish.

BTW, I forgot to say that salt is added to the wash water.

Why anyone in this day and age would still process raw linseed oil, is beyond me. Try using Varnish Maker’s Linseed Oil at WoodFinishing Enterprises. 

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3 hours ago, David A.T. said:

I just took a look in Bonnani's book from 1723.

here is one of the receipt of the italian varnish  : take 8 part of Turpentine, put on fire till it reduce to 1 part....

The current usage is not so far.

Bonanni Italian varnish.JPG

Note : no (washed or not washed) linseed oil in this receipt.

then old evidence of cooking the resin at high temperature could be inside this book (1693) : https://www.amazon.com/Collectanea-Chymica-Leydensia-Maetsiana-Margraviana/dp/1166677524

while it is decribed as a text in Latin it is actually in german.

https://play.google.com/books/reader?id=Lbc5AAAAcAAJ&pg=GBS.PP6&hl=f

I will try to find the corresponding extract. 

 

 

I read a good number of manuscripts, including in old Italian dialects. You have to search in specific chapters about the preparation of the oils. 

In Mary Merrifield 's treatise, though I found transcription/translation mistakes, you can find a whole lot of good infos from older treatises. 

There's a text about how to wash the oil. ( a transcription by Charles Eastlake if I remember correctly). 

After all,

You cannot find everything in books, and some are difficult to interprete though very interesting. Otherwise some of us would stop spending so much time in searching for the so-called holy grail and stick directly to the proper job. 

Having said that, I don't mean to offend you at all. 

Experiments are sometimes the best way to learn. I did a lot of craps and messed a lot with varnish, but it taught me a lot. 

Also, I attended to specific varnish making and varnish related courses. And served once as an assistant to François Perego for example. 

Those courses are a good starting point as well. 

And the first thing to think about is always safety and preparation, as cooking varnish could be very dangerous. 

Friendly. 

Dave. 

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