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Berl Mendenhall

Cooking Colophony Down For Color, Low and Slow?

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Just a guess... if oxidation is important, then hot and fast might not give it enough time to happen.

 

 

On the temperature controllers, relays, thermocouples...

I'm sure it's a highly capable system, and not expensive at all.  I have all the parts I need to hook it up, but haven't gotten around to doing it yet.  One word of caution:  the instructions and manuals appear to be written for folks with experience in feedback temperature control systems (and even from China, perhaps).  I like to think of myself as reasonably techinically competent, but these manuals are really pushing my comfort zone.  Like violinmaking, it's probably less daunting once you get through it a few times.

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Hi John

 

Thank for approaching to the most easy way.
I have a place outide home; a big barbacue with side walls and chimney that would be a secure place. If would explode nothing could happen (I gess). 
If I put at minimum the heater plate during the night I would sustain the lowest temperature. 
It would be better to test first.
 
In this days outside temp. at night is about 13 cº
 
Also thanks all for advises and ideas.
Regards 
Tango

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Tango, everyone's setup will have different thermal properties, but with my hotplate the colophony would solidify on the lowest setting.

I never cook it completely unattended. I'll put it on first thing in the morning for about 12 hours or so, checking at approximately hourly intervals that all is well, then turn it off in the evening until the next day. Or the next fine day if the weather is not favourable. 

Then I'll clock up another few hours and repeat until I've done about a hundred or so. I've never burned any colophony doing it this way.

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Just a guess... if oxidation is important, then hot and fast might not give it enough time to happen.

 

 

On the temperature controllers, relays, thermocouples...

I'm sure it's a highly capable system, and not expensive at all.  I have all the parts I need to hook it up, but haven't gotten around to doing it yet.  One word of caution:  the instructions and manuals appear to be written for folks with experience in feedback temperature control systems (and even from China, perhaps).  I like to think of myself as reasonably techinically competent, but these manuals are really pushing my comfort zone.  Like violinmaking, it's probably less daunting once you get through it a few times.

Tight temperature regulation becomes a little more difficult with hysteresis in the control loop. With a relay, by the time the thermocouple senses the shut-off temperature and opens the circuit, the residual heat continues to cause over-shoot past the targeted temperature. With a PID controller you can take this into account in the program setup. Even better is pulse width modulating a triac instead of using a relay, enabling a linear control of heat output.

 

However I think this is making things way overly complicated compared to heating over a fire and using a feather to sense the target temperature.

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I have to ask,  instead of cooking long and slow, what's wrong with hot and fast?   And why is a little bit of burn undesireable? 

 

From the varnish section in the bass thread (Roger Hargrave):

 

"The method(s) I used for combining these ingredients was based on two or three further snippets of information. The first of these concerned the length of the colophony molecules. These were not found to have been significantly altered. Accordingly, White had concluded that the colophony had not been cooked at a high temperature. He suggested that it had probably been heated just hot enough and long enough to blend it with the oil and mastic. (His conclusion about the mastic was that it had probably been added as plasticizer.)

 

"In addition to this important observation about the cooking process, at a later date Professor White was asked to examine a particularly red and rather typical Venetian varnish on a violin by Sanctus Seraphin. White was specifically asked to identify the colouring agent. His reply was illuminating. Having examined the instrument he concluded that the redness in the varnish was simply the result of oxidisation, rather that any additional colouring agent. For me personally this was a revelation."

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I have to ask,  instead of cooking long and slow, what's wrong with hot and fast?   And why is a little bit of burn undesireable? 

 

Just believe. If you burn it you will end up with carbon which is black and this will ruin your varnish for sure.

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Here's a dumb question, asked mainly because I can't remember if it's been asked before:

 

Has it been proven that the more famous of the Cremonese makers bought their varnish from others, or is that just a possibility?

 

Because IF they were making their own, I would think the idea of just heating the ingredients as little as possible would be appealing for safety as well as comfort reasons. 

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Could someone post a picture of what it looks like after 100 hrs of slow low cooking? I'd like to see the color. Is there a picture in the Bas thread? If so, I missed seeing it.

My only experience so far has be hot and fast cooking

Fire is just fast oxidation but maybe too fast eh? :)

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Tight temperature regulation becomes a little more difficult with hysteresis in the control loop. With a relay, by the time the thermocouple senses the shut-off temperature and opens the circuit, the residual heat continues to cause over-shoot past the targeted temperature. With a PID controller you can take this into account in the program setup. Even better is pulse width modulating a triac instead of using a relay, enabling a linear control of heat output.

 

However I think this is making things way overly complicated compared to heating over a fire and using a feather to sense the target temperature.

 

A PID controller is certainly helpful.

Even so, I have found a need to use a series of gradually increasing temperature settings below my target temperature to avoid thermal overshoot when initially starting cooking.  (The thermal overshoot is almost certainly due to the way that I have my system set up...)  Once the target temperature has been reached, everything works in a very stable manner.

 

The reason that I went to this system several years ago (see photo below) was because of temperature drift.  Worse still, if the cooker was not running at full (fully open highest setting) it would sometimes turn off, I suspect due to mains voltage variation.  The resin would get cold, harden and then go through thermal overshoot when the system kicked back into life, often a couple of hours after it had turned off.  These problems have disappeared since using the controller. 

 

It wasn't cheap but has definitely been a good option for most of the types of resin cooking that I do.  Having said this, if you are not a lazy cook and have a reliable system, there is probably no need for something like this...

post-24896-0-04388700-1399325361_thumb.jpg

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I always just use a crock pot,

they heat up slowly,

they come with a removable earthenware insert,

they maintain about 250F consistantly,

there is no way they can get any hotter,

it just simmers till the cows come home,

just peek at it once a week or so.

 

Even in the dead of winter zero or so,

just dig a hole in the snow,

throw some insulation around it and forget it for a couple of weeks.

 

For higher temps an old deepfrier seems to work just fine.

 

I like a little venting in the lid.

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A goose feather will "disappear" as it touches the surface of the cooking varnish at 325C.

on we go,

Joe

 
Hi Joe,
 
I had copied and pasted this from one of your post in an old thread, not remember wich :
 
 
"A goose feather, passed over the surface but not touching, will disappear [save for the quill] when the temperature is 273C."

 

Joe Robson

 

 
Just for curiosity and correctness of information, what is the right temperature? 325C or 273C?
 
 
However I prefer to use the thermometer and let the geese keep their feathers....
 
 
Davide
 
 
 
 

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I think it was the Florentine painter Cennino Cennini who talked about goose feathers for varnish cooking, but he may have been doing something else with them. Very nice book I seem to remember, but it has been a while since I waded though it. I think Dover reprinted it. (Cennino d'Andrea Cennini's 'Il Libro dell'Arte''). Yes! Just found it. Apparently still available from those people we love to hate 'Amazon'. 

The Craftsman's Handbook: "Il Libro dellArte": 

As for the Cremonese makers cooking their own varnish, this is highly unlikely. With the amount of wooden buildings in those ancient cities, varnish cooking was almost certainly restricted to outside the city walls. I have no idea where I heard this, (I think from Herr Fischer in Hamburg), but I believe that two women were killed outside the Hamburg city walls by a varnish explosion. Throughout Europe, professions and activities of all kinds were strongly controlled by guilds. In view of the dangers it is extremely unlikely that varnish making would have been carried out within the city walls of Cremona or by violin makers themselves.  

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I have some rosin on the go as we speak here, started up the batch a couple of days ago so it really isn't as dark as I like to go yet, so I can't show a picture of it. 

 

The point of going long and slow is really the key to good colour. Go high in temperature and most probably find a green hue in the finished varnish that is a pain to deal with.  This has gone from straw yellow to golden orange in 2 days. I expect it to be dark red by Sunday.

 

My workshop is in the basement of the building and a friend lives right above it, in the second floor. I cook the rosin in the window sill, she swears she can barely smell the rosin fuming while is toasting, that is how low the temp is. No neighbour has ever mentioned a problem. 

 

I did run amber once and that was fun... NEVER AGAIN. 

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If varnish cooking is done in a fireplace with a solid bottom and a lip at the bottom front, it's not that dangerous. Spills will be contained, and it's not a problem if the varnish or fumes catch fire (small batches). It's an environment which is designed for fire, and was used inside cities all the time. I'm guessing that oil lamps would have posed a much bigger fire hazard

 

Today, when using an electric heating source to cook varnish in a fireplace, it can be a problem to get the chimney to draft properly (not enough heat), so that's something to watch out for. I've stunk up my house pretty badly a few times when I didn't establish a warm air column in the chimney first.

 

Still, probably better to do outside, well away from anything flammable, and on a non-flammable surface (not your wooden deck :lol: )

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If varnish cooking is done in a fireplace with a solid bottom and a lip at the bottom front, it's not that dangerous.

It gets dangerous when you take the (hot) pot of the hotplate. I would refer to the Markneukirchen Stadtchronic of 1706

Markneukirchen Stadtchronic of 8th February 1706 :

1706. d. 8. Febr.: Hans Caspar Reichelt, Geigenmacher hatte einen guten Fürnis Gekocht und da er solchen vom feuer aufhub ihn auff den kalten Erdboden saßte, sprengte die Gewalt der siedenden Materie die oben übergebundene Rindsblasen auf fuhr in heftigkeit zusammen heraus, entzindete sich in Feuer und breitete sich aus, dass es über ihn und zwei andere nebenstehende Personen sich ergoß, welche die Kleider vom leibe mit der haut des Fleisches jämmerlich wegbrand, dass Err nach erlittenen heftigen Schmerzen abends 4 Uhr weil auch inwendig Zunge, Mund und Hals Ganz verbrand war, seinen Geist aufgabe.

Auch wurde noch eine Person unglüchlich, nemlich es heißt ferner: Elizabeth Hausfrau Caspar Schönfelders Beckers und Geigenmachers wurde in Hans Caspar Reichelts Haus geholt, den gutgeratenen fürneis zu beschauen, worüber auch sie mit diese Materie übergossen wurde, ihre grossen Schmerzen dauerten 11 Tage, starb am 19.

My translation:

1706, the 8th Febuary: Hans Caspar Reichelt, Violin maker cooked a good varnish and as he lifted it from the fire and sat it on the cold ground, the power of the boiling material rose over the covering ox bladder and spread itself out with a violence, caught fire, so that it poured both over him and two bystanders, who’s clothes with skin and meat wretchedly burned away, so that he, after suffered dreadful pain, in the evening at 4 o’clock, since also his tongue, mouth and neck were completely burnt, passed away.

Another person was also out of luck: Elizabeth, housewife of Caspar Schönfelder, baker and violin maker was called to Hans Caspar Reichelts house to see the successful varnish, upon which it also poured over her. Her great pain lasted 11 days, died on the 19th.

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It gets dangerous when you take the (hot) pot of the hotplate.

Of course, nothing is foolproof. I leave hot varnish inside the fireplace until it has cooled. One can also be seriously burned by hot cooking oil. 

 

If Stradivari didn't cook varnish in a fireplace, he also had a courtyard which would have been pretty safe (if the neighbors didn't mind the stink).  Again, small batches, and not a huge cauldron.

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I think it was the Florentine painter Cennino Cennini who talked about goose feathers for varnish cooking, but he may have been doing something else with them. Very nice book I seem to remember, but it has been a while since I waded though it. I think Dover reprinted it. (Cennino d'Andrea Cennini's 'Il Libro dell'Arte''). Yes! Just found it. Apparently still available from those people we love to hate 'Amazon'. 

The Craftsman's Handbook: "Il Libro dellArte": 

--

I picked up a copy of this at Kremer Pigments NYC after the MondoMusica show. Interesting read for sure. BTW, Kremer does stock some good books.

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Of course, nothing is foolproof. I leave hot varnish inside the fireplace until it has cooled. One can also be seriously burned by hot cooking oil. 

 

 

Speaking of the dangers of hot cooking oil, each year, in the US,  fire departments respond to more than 1,000 fires related to deep fryers, which also cause 15 million in property damage, not to mention serious burn injuries.

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It gets dangerous when you take the (hot) pot of the hotplate. I would refer to the Markneukirchen Stadtchronic of 1706

Markneukirchen Stadtchronic of 8th February 1706 :

1706. d. 8. Febr.: Hans Caspar Reichelt, Geigenmacher hatte einen guten Fürnis Gekocht und da er solchen vom feuer aufhub ihn auff den kalten Erdboden saßte, sprengte die Gewalt der siedenden Materie die oben übergebundene Rindsblasen auf fuhr in heftigkeit zusammen heraus, entzindete sich in Feuer und breitete sich aus, dass es über ihn und zwei andere nebenstehende Personen sich ergoß, welche die Kleider vom leibe mit der haut des Fleisches jämmerlich wegbrand, dass Err nach erlittenen heftigen Schmerzen abends 4 Uhr weil auch inwendig Zunge, Mund und Hals Ganz verbrand war, seinen Geist aufgabe.

Auch wurde noch eine Person unglüchlich, nemlich es heißt ferner: Elizabeth Hausfrau Caspar Schönfelders Beckers und Geigenmachers wurde in Hans Caspar Reichelts Haus geholt, den gutgeratenen fürneis zu beschauen, worüber auch sie mit diese Materie übergossen wurde, ihre grossen Schmerzen dauerten 11 Tage, starb am 19.

My translation:

1706, the 8th Febuary: Hans Caspar Reichelt, Violin maker cooked a good varnish and as he lifted it from the fire and sat it on the cold ground, the power of the boiling material rose over the covering ox bladder and spread itself out with a violence, caught fire, so that it poured both over him and two bystanders, who’s clothes with skin and meat wretchedly burned away, so that he, after suffered dreadful pain, in the evening at 4 o’clock, since also his tongue, mouth and neck were completely burnt, passed away.

Another person was also out of luck: Elizabeth, housewife of Caspar Schönfelder, baker and violin maker was called to Hans Caspar Reichelts house to see the successful varnish, upon which it also poured over her. Her great pain lasted 11 days, died on the 19th.

Sounds like what happens when cooking methamphetamine goes wrong.

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I think it was the Florentine painter Cennino Cennini who talked about goose feathers for varnish cooking, but he may have been doing something else with them. Very nice book I seem to remember, but it has been a while since I waded though it. I think Dover reprinted it. (Cennino d'Andrea Cennini's 'Il Libro dell'Arte''). Yes! Just found it. Apparently still available from those people we love to hate 'Amazon'. 

The Craftsman's Handbook: "Il Libro dellArte": 

As for the Cremonese makers cooking their own varnish, this is highly unlikely. With the amount of wooden buildings in those ancient cities, varnish cooking was almost certainly restricted to outside the city walls. I have no idea where I heard this, (I think from Herr Fischer in Hamburg), but I believe that two women were killed outside the Hamburg city walls by a varnish explosion. Throughout Europe, professions and activities of all kinds were strongly controlled by guilds. In view of the dangers it is extremely unlikely that varnish making would have been carried out within the city walls of Cremona or by violin makers themselves.  

 

The feather thing is common in old italian texts. Perhaps Cennini was the first to print it?

 

As for the varnish cooking outside town, maybe this helps?

 

Text below printed in 1899, sorry I don't have time to translate now, maybe later on tonight. but briefly, it speaks about a place outside Florence's city walls where people would cook varnish, because they where not allowed to do it in town, because of frequent explosions which could be a cause of fire.

 

Risalendo un po' la strada poiché quando le mura si avvicinavano alle porte il piano era in discesa, e continuando per la Porta a Pinti, in faccia al Vicolo della Mattonaia che metteva in Borgo la Croce si scorgeva il grazioso villino Ginori con le due cupolette a squamme gialle e turchine, ed in quel punto delle mura esisteva un vuoto ad arco come una gran nicchia tutta nera, e piena d'una fuliggine lustra come unta. Quello era il luogo dove i verniciatori, i mesticatori e i legnaioli, andavano a far le vernici, poiché non era permesso di farle in città, a causa dei frequenti casi in cui scoppiavano i matracci, e che potevano esser causa d'incendi.

In cotesta località, quasi deserta e fuori di mano, andavan pure i carradori a piegare i cerchioni delle ruote dei barrocci e dei carri; operazione che si faceva con sistemi molto primitivi, poiché facevano in terra un gran cerchio di grandi scheggie fatte coll'ascia nel modellare il legname, e vi mettevano sopra i cerchioni, che con delle grosse morse piegavano quando il ferro era rosso.

 

FIRENZE VECCHIA

STORIA - CRONACA ANEDDOTICA - COSTUMI

Giuseppe Conti - (1799-1859)

 

https://archive.org/details/firenzevecchiast00contuoft

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