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How to make use and read a step test "wedge"

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How to make use and read a step test "wedge"

Postby Ellitepress » Wed Jan 25, 2006 8:39 am

What you need to make a step test:

1) A UV light blocking film or paper (red or black construction paper, or a sheet of masking film like ruby or amber masking film) We will call this the "blocking sheet"

2) A good printed positive with several block of repeted art - if you use an inkjet with a rip you are all set - if you use a toner based printer with vellum or frosted film make sure you spray a darkener on the toner (and cross your fingers).

3) One coated screen for each mesh you want to test

4) An exposure unit

5) patience - this is going to take a while.

Step one:

Make a guess at how long the exposure time will be and AT LEAST DOUBLE THAT TIME! - that is your total time range - now devide that time by the number of blocks you have on your positive. We will call that small unit of time the "block time".

Tape the positive onto the screen

Place the screen on the exposing unit and expose it for one of the "block times".

Step two:

Remove the screen from the exposure unit.

Tape your "blocking sheet" over ONE of the blocks on your positive.

Return the screen to the exposing unit and expose for one more "block time.

Step three:

Repete step two by advancing your "blocking sheet" over an additional block on the positive - make sure the sheet covers the new block AND the other blocks that were covered from before.

Repete this process until you expose the last block.

Remove the screen from the exposure unit and take off the positive and the blocking sheet.

Step four:

Wet the screen front and back with water from a hand sprayer or a water hose and keep wet for about 3 to ten min. (do this out of direct or strong reflected sunlight)

While still wet look at the screen - if you are using a diazo or dual cure emulsion you will be looking for a time where the diazo no longer discolors the emulsion and the steps for longer times have no color changes - if looking at a pure photopoly this change is harder to see and you will need to look into the emulsion with a strong light in the background.

The point right past where the emulsion stops changeing is the best exposure time - as the UV light has exposed and hardened all the emulson layer.

While an exposure calculator takes lots less time - a step test can be more accurate - and the combo of BOTH a calculator (to get close) and a step test will get you an exact time down to seconds.

BOTH a step test and or an exposure calculator will save you THOUSANDS in time, effort, and product......
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Postby Anonymous » Sun Feb 26, 2006 4:46 am

Thanks for the low down on a step wedge test!

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