# what does emulsion do when its bad?



## 4taylormadetees (Jan 9, 2009)

what does emulsion do when its bad?can you look at it and tell?or does it not work right?


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## JeridHill (Feb 8, 2006)

You can't really tell by looking (as long as it was sealed). If the emulsion doesn't perform like it used to and you increase your times and still can't get a good burn, then most likely it's bad. You can place the emulsion in a refrigerator to make it last longer.


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## 4taylormadetees (Jan 9, 2009)

when i burned the image .it just it blew out the image to easy.
is in the fridge with food ok? how many months will it last then .


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## TYGERON (Apr 26, 2009)

4taylormadetees said:


> what does emulsion do when its bad?can you look at it and tell?or does it not work right?


What does it do when it's bad?
It doesn't behave like a good little emulsion should.

With some you can kinda sorta look, with most it just won't work right. The only true way is to try it according to the emulsion type, light source, mesh line count, number of coats, humidity etc. Use an exposure calculator. An emulsion's shelf life varies with a lot of different factors. And the guidelines given by the manufacturer are not hard set times. And there are generally significant life differences between pure photopolymers, diazo and dual cure emulsions.
And refridgerator is cool to store (no pun...well, yes pun) but don't let it freeze.


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## RichardGreaves (Nov 7, 2006)

4taylormadetees said:


> when i burned the image .it just it blew out the image to easy


I'm guessing you meant to write the 'stencil dissolved in water', rather than the image area. The un-exposed image area is supposed to dissolve with water.

There is one universal test for all stencils - Either it dissolves, or it doesn't. 

*Exposure is easy*
If it dissolves with water, UV energy didn't cure/harden it. The proof is in your screen. If your stencil doesn't survive development, you didn't do your part of the process by exposing it for long enough.

*Steak*
You understand exposure from cooking. If your uncle George likes his steak well done, what do you think happened if the inside is all pink? Basic adhesion has to do with UV energy moving all the way through the stencil to completely harden/cure it. If it "seems" to be under or over exposed, you aren't measuring your exposure, you're guessing.



4taylormadetees said:


> what does emulsion do when its bad?
> 
> can you look at it and tell?
> 
> or does it not work right?


It's clear that you aren't monitoring or measuring your exposure. 

*Measuring Stencil Hardness*
Without a step wedge test positive, you can't really tell if you actually cross-linked all the sensitizer. The best exposure test for stencil hardness is a US$10 Stouffer T-2115 21 Step Transmission Gray Scale.
Transmission Step Wedges Transmission Step Wedges

A transmission gray scale is a small film positive with darker and darker filters next to each other in steps. This is a standard photographic darkroom test positive that's been used since the 1930's.

When you have it on an unused corner of the stencil as you expose, you'll get a simulation of 21 different exposures to the stencil and you get visual feedback that shows how well your stencil is cured.

When you develop the stencil, areas that didn’t get enough exposure will *dissolve with water *and rinse down the drain. Aim for a Solid Step 7 that stays in the mesh and survives development. More exposure will make your stencil more durable and less will make the stencil less durable.

You will know when to change your exposure to get back to a Solid Step 7. You will notice if it washes out differently and you will know your lamp or stencil has changed. 

*How emulsion goes bad*
Emulsion doesn't "go bad" like a vampire at sunrise, (UV humor), it begins to react slower to UV energy. You can't taste it like milk that's gone bad but, the Lot#/birth date is one of the variables you should use in you judgment in the future. If you didn't use up the container in 12 months, you need to buy smaller next time, just like milk. A gallon of milk is a great value per ounce, but if you can't use it before the expire date, it's a waste.

When emulsion or film is "fresh", it's exposure speed is more stable and dependable -If it exposed in 4 minutes before, it might take longer to achieve the same cure as it ages. 

Diazo sensitizer mixed into wet, raw emulsion emulsion is like lighting a candle, it gets used up over time. The pot life of mixed diazo emulsion is about 4-6 weeks before it loses it's freshness, exposure sensitivity fluctuates and factory promised resistance to solvents or water degrades. 
It still works - just slower.

SBQ sensitizer that's added by the factory isn't effected by water and has an 18 month shelf life. 

*Diazo does not spoil like food*
Screen makers often read on the label of any emulsion to store it in an area not to exceed 85°F - so they react by putting emulsion in the only cool place they have, where at 42°F, it's 10°F from ice cream.

Yes, cold will slow almost any chemical reaction but
putting the emulsion in a refrigerator does little to slow down the water absorption breakdown of the diazo sensitizer. You'll feel you did everything you could to prolong it's shelf life though.

*Cold Coating*
Beware that cold emulsion will coat thicker than room temperature emulsion and when the coating warms up it may drip. After a few coating sessions where you have to wait for the emulsion to warm up (like cold butter), and the varying coating effects you get when you coat at different temperatures.

*Homework

How does the Stouffer T-2115 work
*http://www.t-shirtforums.com/screen-printing/t116047.html#post681851

*How to measure exposure*
http://www.ulano.com/FAQ/FAQexposure.htm#Q1

*What's the difference in emulsion?*
http://www.t-shirtforums.com/screen-printing/t116047.html#post681482


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