 Re: How to know if your emulsion has gone bad
You give us little to go by. There are dozens of types of emulsion.
Trust your batch date. If you tell us what kind or brand or model I could be more specific. All emulsions have a shelf life.
Diazo sensitizer types. It is the diazo that goes bad after a year on the shelf and it will lose power. You can buy new sensitizer.
After you add diazo to emulsion, the water breaks down the diazo so you have 6 weeks to coat, then another 4 weeks to expose.
Dual cure emulsions have 2 sensitizers. Sometimes this is diazo and the rules above apply. The other sensitizer is created at the factory and will age and fail after 18 months so keep an eye on the batch date.
SBQ or pure photopolymer emulsions usually have an 18 month shelf life.
Shelf life is based on ideal storage conditions. Milk has a 3 week 'refrigerator life'. If I leave it in the sun all afternoon at the picnic, I don't think it will last 3 weeks.
If you need to check if the milk is bad, you smell it. If you expose your stencil for a "known amount of time", and it washes out of the mesh, it's lost sensitivity.
Are you having a problem with the emulsion you have right now? If so, tell us the symptoms, but emulsions are easy. If they wash out, they haven't gotten enough UV energy to cross link the stencil. If they don't wash out, something cross linked them.
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How are you measuring? retired Ulano Technical Support
Screen printing since 1979 - SGIA Academy Member
Last edited by RichardGreaves; February 18th, 2008 at 07:16 PM.
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