I’d like to understand the difference between a screen that’s exposed and a screen that’s exposed and emulsified. I’ve read that a screen that’s been exposed lasts until it deteriorates and can be kept for a long period of time, whilst a classic emulsified screen lasts a week.
OK, let me clarify: to expose a screen it needs to be emulsified first.
This is the sequence of operations:
1) Emulsify the screen, in other words spread a layer of emulsion over it and leave it to dry in the dark;
2) Expose the screen, put the film onto the emulsified screen, expose all of it to UV light and then prepare it in water.
A screen that has only been emulsified, i.e. it has only undergone step 1) above, can be kept in the dark for a maximum of 10 days, because the emulsion, despite being dry and in the dark, tends to harden.
A screen which has been emulsified and exposed lasts for a very long time, until it deteriorates through use, i.e. after thousands of prints.