How to seal petri dishes

Written by kent page mcgroarty
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How to seal petri dishes
Find effective methods for sealing a Petri dish. (Bacteria Colonies image by ggw from

Petri dishes are shallow, round dishes with loosefitting covers used to culture bacteria and other slow-growing organisms. They are either made of plastic or glass and are often sealed with broad rubber bands, paraffin, cellulose tape or adhesive tape. Such methods are considered cumbersome and ineffective techniques for sealing a Petri dish, according to "A Simplified Method for Sealing Petri Dishes" by Mary E. Powell, the Henry Phillips Institute, University of Pennsylvania. Powell writes that the use of a polythene transparent plastic envelope is a much more effective method.

Skill level:

Things you need

  • Polythene transparent plastic envelope
  • Scissors
  • Two pieces of cellophane
  • Electric flatiron

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  1. 1

    Procure a polythene transparent plastic envelope. Sites like offers a list of where to purchase such envelopes, or try browsing sites like and These envelopes are manufactured by assorted companies as flat tubing with varying degrees of thickness and diameter, so do some research to find out which brand best suits your needs. For observation purposes, Powell recommends using a tube envelope that is an inch or two longer than the dish.

  2. 2

    Cut the plastic tubing to desired length if needed. Insert the inoculated Petri dish into the tube. Cover both ends of the tube temporarily with cellophane.

  3. 3

    Seal both ends of the tube with an electric flatiron. The cellophane will protect the plastic from melting as you seal it. Colonies can either be studied through the plastic or taken out for observation, then returned to the tubing and sealed.

Tips and warnings

  • Shrink seals, or colourless transparent cellulose bands for sealing Petri dishes and test tubes, are another effective option for sealing Petri dishes. Try laboratory stretch film available through science supply sites like Electron Microscopy Sciences. Such film is heat-resistant and solvent-proof.

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