Requirements for magnetic stirrer

Jerevan · Jun 10, 2008

I am still pondering emulsion making, slowly amassing the gear and needed chemicals. What are the requirements for a magnetic stirrer, such as minimum volume, etc? Is a stirrer without a heater useless or is it possible to use with, say, a water bath and the emulsion in another beaker? If not, does a heaterless stirrer have any other photographic use?

Mike Wilde · Jun 10, 2008

they can be adapted

I have what was once a heaterless magnetic stirrer. I also had a salvaged 'bunn' commercial coffee pot warming stand. I extracted the heating element, and bolted to the underneath of the aluminum top plate of the stirrer, clear of where the motor spins the under platform magnet.

I also have a temperature controller, but have not yet integrated it into the heater control circuit. Right now I use the full on heater to keep developers hot while I wait for glycin, or crushed crystals of metol to dissolve..

The plan is some day to use this for emulsion making experiments, but in the mean time I work full time, as does my wife. She also studies part tiem, and then there are my 5 and 8 year old and thier activities. So perhaps the experiment may have to wait a decade or so.

dwross · Jun 10, 2008

Jerevan said:
I am still pondering emulsion making, slowly amassing the gear and needed chemicals. What are the requirements for a magnetic stirrer, such as minimum volume, etc? Is a stirrer without a heater useless or is it possible to use with, say, a water bath and the emulsion in another beaker? If not, does a heaterless stirrer have any other photographic use?

A waterbath that you have heated on another unit works just fine. The only disadvantage is that you will need to babysit the temperature a bit. Have some very hot water available to add to the waterbath as needed. The larger the volume, the longer it will hold its heat.

I make my waterbaths from glass storage bowls with tight plastic lids. (Pyrex brand is my favorite). You will want a bowl that is as high as about 1-2 cm shorter than the beaker you intend to use. Set the beaker on the center of the plastic lid and trace a line around the bottom. Then, cut the hole a bit smaller and cut little notches around the circumference. These 'fins' help hold the beaker down so that it doesn't float up in the waterbath before it's filled and heavy enough to stay down on its own. Punch a hole in the lid towards the outside edge to insert a thermometer.

A magnetic stirrer is very handy if you start to mix your own chemistry.

Best of luck and fun,
d

Kirk Keyes · Jun 10, 2008

Take a look of Denise's water bath as she described above at the bottom of the page here:
http://dwrphotos.com/blog/Section13/GlassNegatives.htm

What would be nice is a container that has a drain/spigot so that you could drain the water when it gets too cool and then you could pour more hot/warm water in from the top.

Yes, as mentioned, you can stir a lot of hard to disolve chemicals into solution with a plate stirrer. But keep an eye out on the'bay for a used stirring hotplate. It even helps with those hard to dissolve chemicals as it heats the solution to help them dissolve in.

Kirk

PS - Mike, that looks like a lot of work. But I like your approach!

Kirk Keyes · Jun 10, 2008

Jerevan, you asked about minimum volume - I'm not sure what you mean, as if you can put the beaker on the plate, you can stir it. But a plate with a 5x7 or so top is a good all-round size. They do make mini-stirrers that are say 4 inches square, but they are really not for the sizes of containers you would most likely want to use for general photo or emusion purposes. They make multi-stirring plates that can stir 6 beakers or so at a time, but that's definitely overkill for this use.

Jerevan · Jun 10, 2008

Thanks for all the input. The cheapest stirrer I could find has a capacity for 1 litre. I am thinking of making emulsion to coat onto paper at first, for 5x7" negatives, but it is really a long way to go from where I am now. But at least I know a bit more about magnetic stirrers!

Marc Akemann · Jun 10, 2008

Interesting to me, too. Over the weekend I picked up a magnetic stirrer as part of a purchase of three boxes of photographic equipment, chemicals, paper, enlarger, etc. First estate sale I've ever been to and it was kind of weird going through other people's stuff, but, if anyone wants the stirrer, it's theirs. I'll probably never use it. It's an LKB Magnetic Stirrer Type 6901 A. Made in Sweden. It's set up for 115V. You pay for shipping. Weighs about a pound, pound and a half. If no one grabs it soon, I'll put it on the APUG Classifieds. If someone wants to give me money for it, all the money will go to APUG.

Marc

Marc Akemann · Jun 11, 2008

We have a winner for the LKB Magnetic Stirrer.

Marc

Photo Engineer · Jun 12, 2008

As for volumes, with gelatin present the viscosity makes it difficult to go above about 500 ml with good stirring. So, I use graded magnetic bars in 2" down for 500 ml down to 100 ml volumes.

Above 500 ml, I don't use magnetic stirring. Instead, I use a prop mixer, but I can add to the mixing at the bottom by using a prop mixer and a magnetic stirrer.

The convenient thing about magnetic stirrers is that they often come combined with a hotplate, so you get a 2 in one.

PE

Aurum · Jun 17, 2008

^^^WHS^^^
In my experience, mag stirrers are great for lower viscosity stuff, but a right royal PITA once it gets thick. I'd recommend a good triangular cross-section flea for stirring the thick stuff as its less likely to break away and go clickety clackety (PE knows exactly what I mean)
Prop stirrers are also good, but REAL men use a Silverson!!!!!!

My only other point to raise is that if you're using a stirrer hotplate, (you can get thermostatic controlled ones with a temperature probe), but otherwise don't heat to vigorously if you're using glass beakers. The bottoms tend to pop off if unevenly heated. This is where a water bath comes in handy.

For work I use stainless steel beakers, as I have to work in a glass free environment. These may be OK for a water bath, but might not be appropriate if you're handling silver salts and the like

Oh and a tip for those wanting to dissolve those hard to dissolve crystals: Get a ultrasonic bath off ebay (The sort used for cleaning jewellry) Once you've used one you won't go back. If you can handle the noise that is

Photo Engineer · Jun 17, 2008

Using SS beakers with temp control hot plates is not advised by most manufacturers. IDK the full reasons for the problems, but I do note ultra rapid heating of the base wrt the top of the solution/beaker and I notice that radiation from the top causes a severe temperature gradiant from top to bottom.

Actually, I wish I could use a Kodak mixer, but I think that they would shoot me if I tried to get one out of the plant. That beats them all, and there is nothing like a steam CTB for temperature control with a cold water sparger on the cold side. Makes me homesick thinking about it.

PE

Aurum · Jun 17, 2008

Must admit thats news to me. I've used stirrer hotplates with stainless steel beakers , and a temperature probe which sits in the mix in a commercial development lab for toiletries making hot mix emulsions. Nothing in the manual about that.
The hotplates get hammered daily 5 days a week, Minimum 8 batches of up to 5kg each a day, and the only failures we've had are due to operator stupidity.
The most common failures are: Burning through the probe cable by letting it drape over the hotplate, and using a prop stirrer and catching the probe around the shaft and corkscrewing it!
These are the direct heated metal topped ones mind, not the rinky-dink halogen ones, and they're not designed for single degree accuracy, just enough control to get an oil phase up to 70 celsius, and hold it there without the temperature shooting above 100 and filling the lab with smoke
You're obviously using high quality scientific ones instead, designed for exact control, and good stability

I agree about the steam bath about being controllable, but they're too slow in heating for my work.

Interesting to compare how another industry works

Photo Engineer · Jun 17, 2008

I have 2 Corning mixer hot plates with controllers. Both have in the instructions a warning not to use SS for the container. I have tested them and they work, but the heat gradient is much larger than with glass.

PE

Kirk Keyes · Jun 18, 2008

Perhaps it's the stainless dampens the magnetic field somewhat and reduces the stirring capacity. My Corning plate seems to wirk fine with stainless beakers, but I've heard people say not to use them.

Requirements for magnetic stirrer

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