Posted 25 January 2006 - 09:42 PM
just let a little air in the ziplock
Posted 28 July 2007 - 03:40 AM
Step Four: Learn to work with Parafilm
First off, Parafilm is the SHIT for sealing stuff. It is indispensable with Petri dishes and slants. Plastic wrap and/or masking tape can work but they are a POOOOOOOOOR substitute.
Parafilm sticks to itself – that is why it makes a good wrap for the plates. Parafilm also makes a stack of plates stick together! Pull them apart gently and you won’t have an issue. Jerk them apart and one or the other might tear its seal loose. Pull plates apart gently!
Don’t worry about buying a whole roll of Parafilm for your first time out (whole rolls are expensive, but they last FOREVER). Folks on eBay will sell you small amounts (at inflated prices, but cheaper than whole rolls) that are perfectly usable. HINT: on eBay, you are buying “stuff that will be used to mask a plastic model’s canopy/wing while painting.” If you look for mycology Parafilm on eBay…well, just go ahead and lube up yer butt. You are about to get bent over.
As a total side note, if any of you do paint miniature or R/C airplane models, Parafilm is fucking AMAZING as a masking material for making lines/shapes. Parafilm will NEVER (and seriously, I mean NEVER – even on foam) lift the undercoat color when you remove it. Parafilm is really neat shit.
Regardless, a strip of Parafilm (cut from a roll) looks like this (this is enough Parafilm for 10 plates):
The strips on the right are what you will use for sealing the Petri dishes.
You MUST learn to prepare/stretch the Parafilm before trying to use it.
Parafilm does NOT come ready to use. It sounds hard to “prepare” it, but it is really quite easy.
Basically, you slowly (about 3 seconds) stretch the Parafilm to almost three times it’s original size while grasping both ends firmly. As it stretches, you can see it change visual qualities. You can see the “thick” spots disappear and stretch out. This is what you are shooting for: After all the “thick spots” disappear, you have a ready to use piece of Parafilm.
If you stretch past all the “thick” spots stretching out and disappearing, the film will tear. Torn film should be wadded up and disposed of.
It should look something like this (pardon the shots – best I could do)…
Removing the paper cover and expose the Parafilm:
Get a GOOD grip on both ends and start pulling slowly and equally in opposite directions:
As it stretches, note how parts of it change appearance. To the right is an area that hasn’t stretched enough. To the left is an area that has stretched enough. Compare this pic to the pic below and you will see the “thick area” to the right disappear:
Note how uniform it looks – almost ready to use; hold the current stretch for about 3 seconds to “set” the stretch:
Edited by Sidestreet, 20 August 2015 - 08:44 AM.
Posted 28 July 2007 - 03:52 AM
Step Six: Seal the plates and store them
This is where the Parafilm comes into play.
You already spent some time learning to stretch and wrap with it, right???
Parafilm is really critical to sealing and keeping your plates clean (uncontaminated) for the next few months, stored in the fridge, until you are ready to use them. If you are gonna go this far, don’t skimp on sealing with masking tape/plastic wrap.
Pulling plates out of the crisper 2 months later, when you need them, and finding them brown/grey/green with mold just sucks.
Start out by making sure the agar is hard. If is still flowing at all on the plate, wait another 15 minutes. The agar MUST be completely solidified before the plate is Parafilm sealed.
Stretch a single strip of Parafilm. Wrap it around the side of the plate and grab it, on the top and bottom of the plate, with your fingertips:
While holding your fingertips down (mashing the film onto the dish top/bottom) stretch the Parafilm and wrap about 1/3 of the dish. Keep the Parafilm parallel to the dish at all times. It is critical that the Parafilm overlap both the top and bottom of the dish all the way around:
Keep stretching (gently stretching) and wrapping. The Parafilm should be slightly taunt the whole time, so it makes a good seal with the plate. Don’t stretch it too taunt or it will tear – just keep it tight:
At the end, just mash the edges of the Parafilm to itself. Now roll the plate in your hand to mash the sides of the Parafilm down all the way around.
HINT: Practicing with your Parafilm is incredibly important. DON’T have your first experience with it inside your glove box…voice of experience…
An “average” strip of Parafilm will wrap an “average” Petri dish two full revolutions plus some spare. If you don’t get two full layers of Parafilm around the plate, use additional pieces. You can’t put on too many layers – but you can put on too few. One layer is NOT enough for effective sterile storage.
One layer of Parafilm is designed to breathe. Two layers are designed to be a seal. Keep this in mind when using Parafilm.
Parafilm can be used in this exact same fashion to seal slants or flasks or jars (or just about anything else with a weirdly shaped opening). Just use two layers to seal or one layer to “breathe.”
PARAFILM WILL NOT SURVIVE THE PRESSURE COOKER. IT WILL MELT AND MAKE A HORRIBLE MESS. DO NOT PRESSURE COOK PARAFILM.
Edited by Sidestreet, 20 August 2015 - 08:45 AM.