[kc6789]

I just changed around my exposure unit so the screen is closer to the lights.

I tested a 110 mesh screen and a 230.

I exposed from 1-8 minutes and each minute looks like same for both screens.

WTF!


Sent from my iPhone using TShirtForums

 

[Blackwater]

Stouffer 21-Step Scale
Stouffer Grey Scale

 

[BroJames]

What is your exposure unit including wattage and distance? What is the same?

1) Did the emulsion on all the 8 segments wash out including areas that are not supposed to wash out?
2) Did all segments wash out OK?
3) Are you unable to get a washout on all the 8 segments?

 

[RichardGreaves]

The core responsibility of the screen maker is to able to judge exposure time with tests. It takes a lot less time to actually test a screen, than for me to actually type up these notes.

If I was at your shop today, I would still have to make a test.

Diazo sensitizer color change
When you test different exposures (like any cooking process), stencils with diazo sensitizer will change color during exposure because the yellowish diazo will actually degrade from UV reaction and the stencil will return to the color is was before you sensitized it.
When you don’t see any more color change, all the diazo is used up, the stencil has reached it's saturation point, and more UV energy just doesn't change it any more.

Don’t waste any more time exposing it, if it won't change any more.

If you are using a pre-sensitized emulsion, there is no color change so you can only judge if the stencil survives or not - which is why you want to use a standard Stouffer 21 Step Gray Scale to simulate 21 exposures on every screen you expose for the rest of your life.

Your goal for starting is to have a Solid Step 7 survive the developing process.

Homework
http://www.ulano.com/FAQ/FAQexposure.htm#Q1

 

[kc6789]

Each minute, or segment looks perfect! But which minute do I choose to expose at?


Sent from my iPhone using TShirtForums

 

[RichardGreaves]

As I wrote in April, exposure is easy.
http://www.t-shirtforums.com/screen-printing/t115829.html#post679917

If the stencil dissolves in water, there wasn't enough reaction with the sensitizer to UV energy to hold it in the mesh.

Diazo gives you a color clue as the diazo reacts with UV energy, but the US$10 standardized Stouffer T2115 Guide simulates 21 different exposures with known filters and if step 7 survives, you have a standard durable stencil on an SBQ or diazo stencil.

I assume if you are looking for change, you are looking for color change rather than survival of the development process.

If you see no change in all your stepped exposures - and they survive, you could have a durable stencil for printing with less exposure.

 

[BroJames]

Each minute, or segment looks perfect! But which minute do I choose to expose at?


Sent from my iPhone using TShirtForums

I use to go with the 2nd or 3rd longest exposure times that produces sharp and clear edges after the wash out. Later, I use the 2nd and 3rd lowest exposure times with the sharp edges. This is if you no other tools to test for proper exposures.