Varnish cooking / safety question


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Hello,

I would like to know if there is any problem, cooking Linseed oil/Colophony type varnishes in corcked erlenmeyer flask. 

I cook till ~280 C and I am using a simple electric cooking plate (so tempereature let's say that has not so much stability -- it is not like pro magnetic/heat plates that are used in labs). (By the way how can I check temperature in a closed flask? I have an infrared thermometer.)

Is it safe or am I making a kind of "bomb" by heating oil/resin in the absence of oxygen?

 

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Your first problem is that your 280 C is 536 F, and your cork will burn. You can measure the temperature inside the flask with a temperature probe, but without stirring, the temperature of a viscous fluid will be uneven, and will be much hotter at the bottom. I doubt that the IR thermometer would give useful results.

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1 hour ago, Nik Kyklo said:

Hello,

I would like to know if there is any problem, cooking Linseed oil/Colophony type varnishes in corcked erlenmeyer flask. 

I cook till ~280 C and I am using a simple electric cooking plate (so tempereature let's say that has not so much stability -- it is not like pro magnetic/heat plates that are used in labs). (By the way how can I check temperature in a closed flask? I have an infrared thermometer.)

Is it safe or am I making a kind of "bomb" by heating oil/resin in the absence of oxygen?

 

 

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Several suggestions:

1. I don't think a cork will contain the increase in pressure from the varnish off-gassing. Or if it does, the container may not handle the pressure. If instead you put a small hole in the cork, I'm pretty sure that the off-gassing will result in the flow going only outward.

2. Use a sand bath or a large metal plate between the heating coil and the jar. An electric coil distributes heat so unevenly, that this can crack even labware. Nor do you want hot spots in your varnish, because these will process at a different speed than the cooler areas. Also, you want a physical barrier between the heating coil and the off-gas, to reduce the chances of the gas reaching the coil and igniting.

3. Do this outside.

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1 hour ago, FiddleDoug said:

Your first problem is that your 280 C is 536 F, and your cork will burn. You can measure the temperature inside the flask with a temperature probe, but without stirring, the temperature of a viscous fluid will be uneven, and will be much hotter at the bottom. I doubt that the IR thermometer would give useful results.

Thank you. Exactly. I was thinking of that. Silicone corks give a range to 240 C. Is the solution to buy a flask with a NS 29/32 joint?

52 minutes ago, David Burgess said:

Several suggestions

01 - Thank you 

1 - Does oil produces so much gasses and high pressure, with abscence of oxygene, in order to explode? I never practically heated oil that way.

2 -  "large metal plate between the heating coil and the jar" --> I have it already

3 - Yes.... My wife does not let me to "cook" around our house.... if she smells a drop of cooked linseed oil, I will stay locked outside...  {One reason more to find a way to cook without smell and fumes!} 

 

59 minutes ago, MikeC said:

The best type of container to use would have tall straight sides and a large opening.  

Thank you. I have wide mouth erlenmeyer flask but I do not use it a lot. An old small cooking pot is fine for normal cooking.

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Just my two cents: I use lab glass beakers for cooking varnish and cover them with aluminum wrap if I want a lid. I would personally not use an Erlenmeyer flask because I think it would make it difficult to deal with foaming/frothing. It would be difficult to stir the varnish in the flask and the taper toward the top would make the froth rise very fast (I think).

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"Is the solution to buy a flask with a NS 29/32 joint?" I spent 34 years as a chemist. I would worry about the joint seizing up if any rosin/varnish gets into it. If you're worried about oxygen getting into it, why not just blanket it with N2 (rent a small cylinder). Geigenbauer has good suggestions.

 

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54 minutes ago, Nik Kyklo said:

1 - Does oil produces so much gasses and high pressure, with abscence of oxygene, in order to explode? I never practically heated oil that way.

 

I don't know about oil alone, but I'm pretty sure the rosin will.

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1 hour ago, Nik Kyklo said:

My wife does not let me to "cook" around our house.... if she smells a drop of cooked linseed oil, I will stay locked outside...  {One reason more to find a way to cook without smell and fumes!} 

Become friends with someone who has a large open yard out in the countryside, and go cook there.

Just think how much grief you'd get from your wife if your closed vessel cooked in the house somehow blew up and caught fire.  I wouldn't risk it.

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I remember my first oil varnish cooking down in the basement of the apartment building with hot plate down right on the doorstep potentially blocking my way out. Somehow I lucked without fire and none of 16 neighbors complained :-) I was 15 back then and would strongly suggest do it FAAAAAAAR away from any building.

I wonder if one can heat resin without oxygen similarly to "torrefied" wood (dry or wet process) and if it would also darken...

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5 hours ago, HoGo said:

Isn't standoil made by heating linseed without presence of oxygen? Anyone knows how it is produced?

Stand oil is heated in a vacuum chamber which creates a polymerized linseed oil.   This prevents oxidation and therefore drying. 

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7 hours ago, Geigenbauer said:

 I use lab glass beakers for cooking varnish

I have some of them with handles, too. But I rarely use them.

39 minutes ago, joerobson said:

Cook in a good thick pot which distributes the heat evenly

This is what I am doing. It does not mean that I do not like to try new methods.

 

Bottom line is --> if I want to give a try, I have to find a magnetic/ heat plate, for lab use in order to have stirring and stable/even heating in the same time. 

 

Thank you so much all, for your interest and your time.

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"I have to find a magnetic/ heat plate, for lab use in order to have stirring and stable/even heating in the same time.  "

If you do that, you'll need to go with a glass covered magnet bar. The usual Teflon ones won't stand that temperature. I would also question stirring anything with any viscosity that way. The motors/magnets don't have a lot of power.

 

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7 minutes ago, saintjohnbarleycorn said:

if you cook a small batch, does it shorten the time vs. a bigger batch, is there much difference?

For me, cooking small batches was not so easy and gave inconsistent results. The colophony often ended up with a cold green tinge, which I do not get when cooking a bigger amount.

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Trust the experts in this thread. There is no advantage (and plenty of drawbacks) to cooking varnish in a closed container. 

I do use a laboratory style stirrer/hotplate for smaller cooks, and it's lovely. Very nice to be able to insert a temp probe and have the machine maintain a precise temperature. Makes long, low temp cooks a fairly braindead endeavor.

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6 minutes ago, JacksonMaberry said:

Trust the experts in this thread. There is no advantage (and plenty of drawbacks) to cooking varnish in a closed container. 

I do use a laboratory style stirrer/hotplate for smaller cooks, and it's lovely. Very nice to be able to insert a temp probe and have the machine maintain a precise temperature. Makes long, low temp cooks a fairly braindead endeavor.

Hmmm, that's interesting.  What brand is your stirrer?  I was about to comment agreeing with Doug that the stirrers I've used would not be up to dealing with high viscosity liquids, but perhaps what you're cooking isn't of high viscosity.

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1 minute ago, Mark Norfleet said:

Hmmm, that's interesting.  What brand is your stirrer?  I was about to comment agreeing with Doug that the stirrers I've used would not be up to dealing with high viscosity liquids, but perhaps what you're cooking isn't of high viscosity.

Hi Mark, it's an inexpensive chinese unit, "Four Es" brand. I don't cook anything much above 200C, and the thickest thing I've put in there was larch turpentine. By the time it reached 200C the stirrer had no difficulty whatsoever, even after 24 hours of cooking. 

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