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Measuring of oil varnish heat


tango

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I thought so but after some research I now prefer one of these...

http://www.thermoworks.com/products/thermapen/?tw=AMAZINGRIBS

 

My understanding is the IR guns read the surface temp...when cooking varnish the temp on the bottom is much hotter than the top. I think Brian Lisus has the right tool for measuring the temp while cooking. It is a long probed thermocoupler. It can be see in his QOP video.

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yes Ernie is correct, it measures surface temp, I use one of these, I usually measure before getting close for safety,  stir and measure again, to measure the mix...works great, and I can measure it from a distance which is good....I use it for a ton of things....but Ernie's is probably better....

 

is there a inert material spoon with a digital thermometer? that would rock, I bet in the Bundesrepublik someone makes one ... I've googled "Digital Varnishmaking Spoon" and nothing... :rolleyes: ..Did you know that if you google "Google" you break the internet? :rolleyes:

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You need to be safe.  Get a device that uses a K-type thermocouple that can read up to at least 350 degree C.  You want the thermocouple lead to be at least 2 feet long.  High end devices might be a Fluke meter, but ebay will have all kinds of inexpensive Chinese-built meters that will work well. 

 

It might be hard to believe if you are not a part of the electronic business, but the chip makers have made accurate and inexpensive chips for reading thermocouples available for decades (with built-in reference compensation).  That is why they are so cheap.

 

Mike D. 

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These optical thermometers measure the integrated blackbody emission from the layers that are translucent in the IR. This is called the effective blackbody temperature. It is usually ~37% down to the deepest detectable layer. If the varnish is totally opaque in the IR, the effective temperature is indeed, the surface temperature. If your optical thermometer sees down to, say .3 mm, then the effective temperature is for the layer ~0.11 mm.

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As Mike D states you need something that wlll get you to over 600 F, but I find  precision is not necessary, and just changes in appearance of the the cooking varnish is adequate after enough runs with a thermometer. Recently I've been substituting rosin for fossil copal resin, and similar keys are present, the difference is the lower temp's with rosin. Rosin varnishes are easier to make and are certainly nicer.   fred

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The last batch of the same species of resin that I like  carbonized at temperatures that were fine for the previous batch. Had I used observation rather than temperature measurements  all would have been good and that is what I will do next time. A thermometer can be of use sometimes but understanding the ingredients as a cook might be more use in the long run. The best ever meal I had was in a small local resteraunt run by local women near to the village where Puccini composed in the Summer months...I am quite sure that everything was measured by eye and better for it but the eyes were certain and educated in more than simple measurement

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If you are using any temperature device that involves immersion (e.g., thermocouple or thermometer), it is important to be aware of the required immersion depth.  Anything less than this depth will affect the accuracy of the temperature reading.  The thermometer used by Ernie seems to require a minimum immersion of only 1/8" (3 mm) which is far better than any of the specs for the thermometers or thermocouple devices that I have....
 

 

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 A thermometer can be of use sometimes but understanding the ingredients as a cook might be more use in the long run.

 

Melvin,

Well said.

but also...

A goose feather passed over, but not touching the surface of the varnish will disappear, except for the quill [without flame or smoke] at 325C.

A good immersion thermometer in a metal jacket is better.

Joe

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Just get a glass thermometer that goes as high as you want it to. I've had mine for 40 years. I sometimes think that too much is made of all this varnish cooking. The feather system was clearly used and is mentioned in several books. It is hardly high-tec. I see varnish cooking as I see lazar style violin making. If you want a lazar made violin that is OK, if you want high-tech varnish that is also OK, but I keep asking myself WHY. Neither Koen nor I worked high-tec. We worked carefully and we recorded what we did, but personally I never went over the top with specifications of oils and such. Artist grade cold pressed linseed oil is generally OK wherever it comes from. However, as I have said before always use artist grade. Bio oils are often pressed in presses used for non drying oils. (Also a problem known to the ancients) My advice is to KEEP IT SIMPLE and if it was not available to the classical Cremonese makers why bother. Occasionally my batches go wrong, but I work with a normal hot plate outside. I have the protection (from rain) of a tiny grass house. I also have my thermometer and that's high-tec enough. We do have geese in front of my house, but they need their feathers. I am sure that they did work as high-tec as they could, but because of the high risk of fire varnish cooking was always done outside the city or town walls, remember they were cooking on open flames. Varnish cooking was done by specialists, which is why it is unlikely that violin makers cooked there own varnishes. Having said all this, don’t forget the high-tec fire extinguisher. 

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I am sure that they did work as high-tec as they could, but because of the high risk of fire varnish cooking was always done outside the city or town walls, remember they were cooking on open flames. Varnish cooking was done by specialists, which is why it is unlikely that violin makers cooked there own varnishes. 

 

Exiting Florence, through the Porta a Pinti, there was an arch in the wall with an open space and a recess, all black, and full of a greasy lustrous soot. That was the place where the varnishmakers would go to cook varnish, it was not allowed in the city because of frequent exothermic reactions, which may have been the cause of fires in town.....(loosely quoted from Giuseppe Conti)

 

An  ex-violinmaker friend said that while she lived in Cremona she saw in an exhibit a paper for varnish order or something of the sort from an apothecary, she did not remember who was the maker....anyone seen this? Does it add up?

Edited by carlobartolini
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The real issue with these optical thermometers is what are you measuring. I wonder about the optical footprint, namely where is the entrance beam focused. I could be measuring the hot pot and not the varnish. Also, how deep into the varnish am I measuring.  When I experimented with varnish making I used a high-range mercury thermometer. I moved its bulb around the varnish to get some average temperature.

 

Probably more important are safety items. I wore a leather apron with gloves, face shield,  and a fume mask. Oh what fun.  :blink:

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Hi Fred

 

Where can I read a rosin recipe and what features have this varnish?

 

Tanks

Tango

 

Hi Tango-  The procedure is more or less what I use for making a copal varnish with modifications, such as not having to crack copal before it can be used-

I have to be somewhere in a little while, so I'll try and sketch out what I do and answer anything at a later time.

My cooking set up is simple. A 750watt hotplate, 4 ounce Gerber Baby Food jar to hold the varnish components, a cut down can with some sand to place the jar in to place the jar in to slow heat entrance, a high class temperature probe from Harbor Freight that was given to me, and a homemade venting system.

In making, I mix together 15g dark rosin, 10g Kremer Linseed oil, and anywhere from 2-6 volumes equal to 2-6 peas of Burnt Umber. This is brought up to melt and kept there for around 10min on the assumption that there is a reaction between umber and rosin, similar to when rosin is used as a flux when soldering. There could be no reaction, but I assume there is. I stay under 400F for this and then increase temp to around 500F at which temperature the carboxyl acid fraction is split off the rosin. I'll stay for around 5-10 minutes to reduce the acidity of the rosin, then increase the temp to a minimum of 525F, just about the lowest temp at which the linseed oil internal structure starts to conjugate, form bonds that will accept oxygen and dry when it is spread out. Because the hot plate has a range of off-and-on at least 25 degrees, i'll go between 525-550. keeping a 3/4 inch rim of foam around the periphery.  I'm still not clear on visual keys when the cook is done, right now I rely on the reduction of foam and inactivity of it. One batch that I ran that I just kept letting it go and maybe a higher temp, suddenly blobs started to attach to the wood stirrer, and when cooled and thinned it was  Tack Free (it could be touched without feeling any stickiness) in about 6 hours!  Right now Tack Free point is not completely understood like when making Copal varnish, and is usually under 24 hours. I've just started with rosin, so hopefully I can get an idea of drying times. Anyway, regards the Gerber Baby Food jars, guava, applesauce and cherries are really good. At least you get a desert with your work. 

The color of the varnish starts yellow gold and turns reddish brown in 3-4 coats. The beauty of rosin over copal is the brightness of the varnish, and I haven't filtered any at this point. I definitely prefer it over copal. I'm going to try gum rosin. I've tried a couple of times, and it is lighter, not as interesting as dark rosin. The umber is very necessary, it contains manganese, iron, two strong driers that combine with rosin to make a drier for the linseed oil. Also undoutely provides color. Hope this gives you an idea of the procedure. I can photo my set up and a piece of maple ribbing with varnish samples if your interested, and I can figure out how to get on MN.  fred

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Fred

 

Thanks for the long explanation.

I need a slow reading for comprehension becouse more than control the temperature I need to understand the proceedings. I will copy this and paste in my archive files.

Two questions

Rosin is the same of colofonia? Umber may be ambar?

 

Regards

Tango

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Fred

 

Thanks for the long explanation.

I need a slow reading for comprehension becouse more than control the temperature I need to understand the proceedings. I will copy this and paste in my archive files.

Two questions

Rosin is the same of colofonia? Umber may be ambar?

 

Regards

Tango

Hi Tango- colophony I guess is the same as rosin. Dark or wood rosin is from stumps that are ground up and steam distilled for turpentine and wood rosin. Umber is a color pigment that you can buy in a tube packed in oil, or you can go to a lumber yard and buy it as a powder that is used to color cement. I use Burnt Umber because part of the manganese is driven off Raw Umber, and manganese darkens resins and I think there is an adequate amount to act as a drier.  It is ok to use Raw Umber, i'm just assuming from the little I've done with rosin that the final varnish is a little browner with Raw Umber. Umber is used primarily because it contains manganese, an excellent drier. I suggest you go on the internet and find a source for dark/wood rosin. Don't hesitate to ask questions. We all have started from knowing nothing.   fred

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Just get a glass thermometer that goes as high as you want it to. I've had mine for 40 years. I sometimes think that too much is made of all this varnish cooking. The feather system was clearly used and is mentioned in several books. It is hardly high-tec. I see varnish cooking as I see lazar style violin making. If you want a lazar made violin that is OK, if you want high-tech varnish that is also OK, but I keep asking myself WHY. Neither Koen nor I worked high-tec. We worked carefully and we recorded what we did, but personally I never went over the top with specifications of oils and such. Artist grade cold pressed linseed oil is generally OK wherever it comes from. However, as I have said before always use artist grade. Bio oils are often pressed in presses used for non drying oils. (Also a problem known to the ancients) My advice is to KEEP IT SIMPLE and if it was not available to the classical Cremonese makers why bother. Occasionally my batches go wrong, but I work with a normal hot plate outside. I have the protection (from rain) of a tiny grass house. I also have my thermometer and that's high-tec enough. We do have geese in front of my house, but they need their feathers. I am sure that they did work as high-tec as they could, but because of the high risk of fire varnish cooking was always done outside the city or town walls, remember they were cooking on open flames. Varnish cooking was done by specialists, which is why it is unlikely that violin makers cooked there own varnishes. Having said all this, don’t forget the high-tec fire extinguisher. 

Hi Roger- in total agreement with your observations. When I make a copal varnish I don't refer to temp's because I've done it so many times. However, making a varnish based on rosin is sort of new to me and I find temperatures helpful until I get the hang of it.   fred

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I am not familiar with this unit. What would that be in grams?

Hi Don, Sorry I should have said it is the volume of a typical vegetable pea. I just got into the habit of using that as a measurement not having a scale sensitive to measure small amounts like driers. Fortunately, the amount of umber used can have a wide range, I think it is the temp at which it is cooked has something to do with it. The more umber the lower temps you can work at (I think).   fred

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