Hot plates for varnish cooking

[nathan slobodkin]

My shop hot plate just burned out and I am looking for another one. Anyone have recommendations for a good varnish cooking hot plate at a reasonable cost?

[Don Noon]

Ebay... search for laboratory hot plate.

Or you could use a cheap deep fryer, but they can have hotspots, poor control, and they're a mess to clean up.

[Mark Norfleet]

I got one similar to this on Jackson's recommendation and it is serving me well, at least so far.  I very much like the temperature control on it.

https://www.amazon.com/Inch-Digital-Magnetic-Hotplate-Stirrer/dp/B074CH8VC5/ref=sr_1_3?crid=5MEOOGV20YA&keywords=four%2BEs%2Bhotplate&qid=1653074127&sprefix=four%2Bes%2Bhotplate%2Caps%2C241&sr=8-3&th=1

[joerobson]

1 hour ago, nathan slobodkin said:

My shop hot plate just burned out and I am looking for another one. Anyone have recommendations for a good varnish cooking hot plate at a reasonable cost?

My current favorite.

[Dwight Brown]

https://www.amazon.com/Corning-6795-400D-PC-400D-Digital-Pyroceram/dp/B004DGID7Y/ref=sr_1_5?crid=2DBI9KQK56S56&keywords=lab+hot+plate&qid=1653080585&sprefix=lab+hot+plate%2Caps%2C148&sr=8-5

 

Maybe something like this.  I had this sort of thing in my lab and they worked well and were safe.  It may be too small and overkill as far as temperature control goes.  Joe R. Probably has more experience than anyone cooking the magic stuff. :-)

DLB

[DarylG]

If buying a laboratory hot plate be sure it's rated for use with metal pots. I once saw the top on an expensive Corning hot plate crack while cooking varnish.

A quote from the Cole Parmer website:
"The primary advantages of the ceramic top plate are that it heats quickly and is highly resistant to corrosion. One of the drawbacks is that it does not offer the same uniformity of temperature across the top plate surface that other top plate materials do. Ceramic tops are also susceptible to thermal shock and should not be used when heating metal vessels or sand baths."

[J.DiLisio]

Make sure you get one with a flat plate.  Some are convex to fit glassware. 

[JacksonMaberry]

On 5/20/2022 at 12:17 PM, Mark Norfleet said:

I got one similar to this on Jackson's recommendation and it is serving me well, at least so far.  I very much like the temperature control on it.

https://www.amazon.com/Inch-Digital-Magnetic-Hotplate-Stirrer/dp/B074CH8VC5/ref=sr_1_3?crid=5MEOOGV20YA&keywords=four%2BEs%2Bhotplate&qid=1653074127&sprefix=four%2Bes%2Bhotplate%2Caps%2C241&sr=8-3&th=1

I upgraded to the larger unit, but still recommend either. It is expensive to buy a good lab hotplate, even a knockoff like the Four E units. However, having the control they afford will save you money long term. The magnetic stirring is pretty wonderful, too.

I prefer to cook varnish in borosilicate glass rather than steel, too. 

[Don Noon]

On 5/20/2022 at 10:47 AM, nathan slobodkin said:

My shop hot plate just burned out and I am looking for another one....

Is it the heating coil or the temperature controller that went bad?

It's not for everyone, but if the coil is OK, I'd fix a thermocouple on the underside of the plate and rig it up to an electronic temperature controller.  I use the same temperature controller (actually, I made 2 of them) that can be used on my hotplate, 2 deep fryers for larger batches of varnish, and my wood processing chamber.  The parts for a controller aren't very expensive.

[Jim Bress]

On 5/20/2022 at 5:07 PM, Dwight Brown said:

https://www.amazon.com/Corning-6795-400D-PC-400D-Digital-Pyroceram/dp/B004DGID7Y/ref=sr_1_5?crid=2DBI9KQK56S56&keywords=lab+hot+plate&qid=1653080585&sprefix=lab+hot+plate%2Caps%2C148&sr=8-5

 

Maybe something like this.  I had this sort of thing in my lab and they worked well and were safe.  It may be too small and overkill as far as temperature control goes.  Joe R. Probably has more experience than anyone cooking the magic stuff. :-)

DLB

I used these hotplates when I worked in a lab as well. I just purchased a Corning PC-600D. Wasted a morning because it didn't occur to me to check to see if it was functioning correctly. The one I got doesn't come up to temperature even with nothing on the plate surface.  

On 5/20/2022 at 3:36 PM, joerobson said:

My current favorite.

1500 watts is quite a bit of power. I'm trying to get a hot plate setup where I can use a sand bath and come up to 300 C. Do you think the Cukor can do that?

 

[Don Noon]

42 minutes ago, Jim Bress said:

I'm trying to get a hot plate setup where I can use a sand bath and come up to 300 C. Do you think the Cukor can do that?

The temperature you can get depends on the power, the loss at the source, the conductivity of the sand (and whatever contacts there are on the way), and the loss at the final stage.  I don't think anyone can predict what will happen with anyone else's setup.

It's actually more complcated than that, but I simplified it.  

For these reasons it's best to have a temperature controller with the control thermocouple as close as possible to (or in) the stuff  you want to control.  Good conduction along the way and insulation around everything will minimize power requirements.  My wood processing chamber only uses 400 Watts, and I could probably hit 300 C with it.

[JacksonMaberry]

Quartz sand is better than most earths. You don't want too efficient a conductor probably, it's the diffusion of the selected medium that dissuades hot spots I think.

[Don Noon]

A poor conductor relative to the pot and oil is one way to prevent hotspots... and prevent getting hot at all.  There's the other way: a really great conductive pot, heavy copper, like cooks use.  Then the conduction from the source to the pot can be good without getting hotspots.

[JacksonMaberry]

16 minutes ago, Don Noon said:

A poor conductor relative to the pot and oil is one way to prevent hotspots... and prevent getting hot at all.  There's the other way: a really great conductive pot, heavy copper, like cooks use.  Then the conduction from the source to the pot can be good without getting hotspots.

Absolutely. You can also just not use a cheap-assed heat source. Getting a good quality, thick walled copper vessel is more expensive than a cheap lab hotplate, and doesn't offer magnetic stirring either. 

Historical varnish making texts mention both copper and iron vessels, but often the most recommended are "well luted" ceramic. They were onto the notion of non-reactive labware early on. 

I've cooked a lot of varnish, of substantial variety, on a plethora of heat sources. For my money, I'd rather a set-and-forget solution with maximal control. Your thermocouple plate seems to meet that criteria. My lab plate does the same. The more variables you can limit, the better 

 

[John Harte]

1 hour ago, Jim Bress said:

1500 watts is quite a bit of power. I'm trying to get a hot plate setup where I can use a sand bath and come up to 300 C. Do you think the Cukor can do that?

Don's comments are excellent.

I use a 1500 watt cooker and generally a sand bath.  Even then I have to be mindful of the depth/amount of sand used in the sand bath.  Too much results in having to wait for an unacceptably long time to reach temperatures that I might want.  For a number of reasons I also use a temperature controller of the type that Don suggests.

[joerobson]

20 hours ago, Jim Bress said:

I used these hotplates when I worked in a lab as well. I just purchased a Corning PC-600D. Wasted a morning because it didn't occur to me to check to see if it was functioning correctly. The one I got doesn't come up to temperature even with nothing on the plate surface.  

1500 watts is quite a bit of power. I'm trying to get a hot plate setup where I can use a sand bath and come up to 300 C. Do you think the Cukor can do that?

 

Yes

[Michael Szyper]

No need to worry too much about it. Got an induction plate + heavy Steel pan. No burning issues. Cooks red colophony in 30 minutes.

[Jim Bress]

Thanks everyone for the helpful input. I really can't afford to not give Joe's recommendation a try for the price compared to a lab grade hotplate. Besides, his response was eloquent it left no room to argue.  I'll probably have it from Amazon before I get my refund from the one I shipped out today, and in time to cook this weekend (if it doesn't rain).

Cheers,

Jim

[JacksonMaberry]

2 minutes ago, Jim Bress said:

Thanks everyone for the helpful input. I really can't afford to not give Joe's recommendation a try for the price compared to a lab grade hotplate. Besides, his response was eloquent it left no room to argue.  I'll probably have it from Amazon before I get my refund from the one I shipped out today, and in time to cook this weekend (if it doesn't rain).

Cheers,

Jim

Nice! Keep us posted 

[joerobson]

17 hours ago, joerobson said:

Yes

What kind of pot are you using?

[Jim Bress]

2 hours ago, joerobson said:

What kind of pot are you using?

For cooking colophony down for color I use a SS asparagus pot.

[joerobson]

1 hour ago, Jim Bress said:

For cooking colophony down for color I use a SS asparagus pot.

I like a cast iron deep fry pot.

[charliemaine]

23 hours ago, joerobson said:

I like a cast iron deep fry pot.

Hi Joe,

I was under the impression that you preferred stainless steel over cast iron. Is there a concern about the varnish turning black over time when cooked in cast iron. Why do you like cooking in cast iron?

BTW I ordered one of the Cukor hot plates. How long has yours lasted so far?

edit:  After reading a few older posts you mention that you like to cook the resin in cast iron and colored varnish in stainless. Does the resin darken better/faster in cast iron?

[JacksonMaberry]

Cast iron as used in cookery is "seasoned", by which means a coating of oil is induced on the surface. This is where the non-stick aspect of a well maintained pan comes from. Such a seasoning would be inevitable in a cast iron varnish kettle - linseed oil is the ultimate such coating forming oil. This will prevent iron contamination

[charliemaine]

13 hours ago, JacksonMaberry said:

Cast iron as used in cookery is "seasoned", by which means a coating of oil is induced on the surface. This is where the non-stick aspect of a well maintained pan comes from. Such a seasoning would be inevitable in a cast iron varnish kettle - linseed oil is the ultimate such coating forming oil. This will prevent iron contamination

Gotta love "well seasoned" cast iron...was never sure about cooking varnish in it though.