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Why manufacturers and chemists recommend glass bottles for storing
photographic chemicals has a lot to do with idiot-proof factors. With a little
attention, inexpensive and convenient plastic bottles can be used
for most photographic chemical storage without compromising their shelf life.
Remember: reusing is the best way to reduce waste, recycle and save resources!
This is especially true because many plastic bottles used for beverages,
detergents, etc. do not charge bottle deposit and their recycle rate is
currently very low. The recycling technology of plastic materials are also
currently inefficient.
How to distinguish material
Most consumer plastic products marketed in the U.S. recyclable symbol such as:
and the number inside the triangle, i.e., SPI (Society of Plastic Industry)
recycling rating number, indicates the material used for the part.
It is often the case that the bottle and the cap use different material and
they bear separate signs indicating their materials.
Materials commonly seen in inexpensive consumer products and of interest
for our purposes are:
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| Plastic materials and chemical properties |
| SPI number | material | gas permeability | acid resistance | max usable temp |
| 1 | PET (PETE) | very good | reasonable | 60°C |
| 2 | HDPE | poor | good | 120°C |
| 3 | PVC | very good | reasonable | 70°C |
| 4 | LDPE | very poor | good | 80°C |
| n/a | PVdC (Saran wrap) | excellent | reasonable | 65°C |
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PET (polyethylene terephthalate) is used as a clear (colorless or tinted)
bottle material in bottled water products. It has very small permeability to
oxygen and nitrogen. PVC has slightly smaller permeability to oxygen but
its use is mostly limited for coating and lining.
HDPE (high density polyethylene) has better chemical resistance to
stronger acids than PET and PVC, and higher usable temperature range,
but poorer gas permeability. HDPE also has smaller water adsorption
than PET.
Recommendation
Use PET for developers. Use PET or HDPE for most other chemicals.
If you store acetic acid stop bath in concentrated form, use HDPE.
If PVC coated cap is available, use it by all means.
Even if you use glass bottles to store developers, make sure the caps
are gas impermeable. The plastic caps are often made from LDPE or HDPE
because they are easy to fabricate, especially LDPE is often used where
tear-off cap lock and/or heat-sealing is employed. These materials are
poor choice for stopping developer bottles. Seal the bottle with PVdC or
Saran wrap and then tighten with plastic cap. Reynolds wraps are PVC.
(Most food wraps are probably copolymerized from PVC and PVdC to obtain
certain mechanical properties, but any of these may be used for our purposes.)
Use of wraps are not recommended nor necessary for concentrated acid stop
baths.
My bottles of D-76, Microphen, and various other experimental formula
are still alive and as vigorous in filled and tightly capped 500ml PET
bottles after two years!
Many photo chemical manufacturers ship their liquid developers
in HDPE bottles. They may or may not be coated or lined with gas
barrier material. If you suspect the life of the developer is shortened
because of gas permeability of HDPE, transfer them into PET bottles
(using common practice such as filling the bottles to the top to avoid
air) as soon as you buy them to prolong useful shelf life.
Additional information
Recycling symbols
Plastic resins - Wheaton Science Products
Plastics 101
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How to distinguish material