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Overexposure : your image won't wash out at all or the lines will appear jagged on the image
Underexposing: your image and the emulsion will wash out easily or you will have a layer of "scum" still on the screen
 

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how do I know if my screen is overexposed or underexposed?
As a screenmaker, your first job is to harden the stencil so it doesn't dissolve with water. UV energy needs to move all the way through the stencil to the back to completely harden the stencil.


I want you to put a Stouffer 21 Step Transmission Scale on every screen you ever make for the rest of your life. Expose so you get a solid step 7. You get visual feedback that is the best monitor I know.

They only cost US$6 to US$12 depending on where you buy and properly used, it should last a lifetime.

Then you need to calibrate your designs so that fine lines don't get choked because UV energy can bend and scatter in the stencil making the small openings - smaller.

It may be that you have to make 0.020" lines 0.030" in your computer, so that they finally print at 0.020".

Exposure FAQ of Screen Making Products
 

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As a screenmaker, your first job is to harden the stencil so it doesn't dissolve with water. UV energy needs to move all the way through the stencil to the back to completely harden the stencil.


I want you to put a Stouffer 21 Step Transmission Scale on every screen you ever make for the rest of your life. Expose so you get a solid step 7. You get visual feedback that is the best monitor I know.

They only cost US$6 to US$12 depending on where you buy and properly used, it should last a lifetime.

Then you need to calibrate your designs so that fine lines don't get choked because UV energy can bend and scatter in the stencil making the small openings - smaller.

It may be that you have to make 0.020" lines 0.030" in your computer, so that they finally print at 0.020".

Exposure FAQ of Screen Making Products
great post. Where might I be able to buy a Stouffer 21 Step Transmission Scale? I want to try this.

edit: I found an old post of your where you listed a few places. Thanks!
http://www.t-shirtforums.com/screen-printing/t11860.html#post219000
 

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Internet Sources for Stouffer 21 Step Sensitivity Guide

Video on making a Stepped Exposure Test and other videos
Support Menu of Screen Making Products

Link to the Screen Maker Exposure Kit at Lawson Screen & Digital
Screen Maker Exposure Kit - 301-900-0-KT
Exposure Calculator for deciding how fine a line you can achieve with your stencil, mesh and exposure.

Separately:
Here is the link to the 21 Step Gray Scale
21 Step Sensitivity Guide - 301-905-1-EA

Below, find the Ulano One Step exposure calculator
21 Step Sensitivity Guide - 301-905-1-EA


T2115 Stouffer 21 Step Sensitivity Guide distributors
Stouffer itself
Mishawaka, IN 46544 574-252-5772
Product and Price list

Graphic Arts Supply Hobart, IN 46342
STOU21 Stouffer 21 Step Platemakers Exposure Guide - $9.28 : Graphic Arts Supply, Online Store

Cape Fear Press Carolina Beach, NC 28428 USA
910/458-4647
Puretch photopolymer go to the bottom of the page

Blue Hills Printing Ink and Litho Supply Corp. $6.53
Wisconsin Dells, WI
Blue Hills Printing Ink and Litho Supply Corp.

American Printing Equipment & Supply Co.
Elmont, NY 11003 $7.50
21-Step Sensitivity Guide - HTC134

PressmansPride.com CA Sacramento, Ca 95822
Fully Stocked Distribution Centers: Chicago, IL 60017 Gardena, CA 90248
21 Step Stouffer Scale

Bostick & Sullivan $11.00 Santa Fe, NM 87507-9743
505/474-0890
Bostick-Sullivan :: Beakers, Graduates, Thermometers & Droppers :: Step Wedges - 21 Step Transmission :: Step Wedge - Uncalibrated

Transmission Step Wedge Numbered ½" X 5" Unit Price: 15.95
21 Step Sensitivity Guide 09-0325
Product Details



I would love to hear of other reliable distributors.

Richard Greaves
Direct line 718-943-1338
 

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Factors that determine exposure

Measuring Exposure
It is fundamental that a screen must survive development. With all the variables of screen making that can effect durability & reproduction, complete exposure/hardness/cure is the minimum skill for the screen maker.

Exposure is volume not time
Exposure time is relative. Exposure is like filling a bucket with water. The source determines the time it takes, but like the bucket, the stencil requires a certain amount of exposure to cross-link all the sensitizer.

How long does it take to fill up a 1 gallon bucket with water?? Without knowing how big the hose is, nobody can calculate the 'time' it takes - but I can measure it in the time it takes to make an exposure test

UV-A energy has to move all the way through the stencil to the inside of the screen. Invisible UV-A reacts with the sensitizer to cross-link the emulsion so it won't dissolve with water.

Screen making variables
Mesh tension - low or high
Coating trough size ratio to mesh open area
Emulsion sensitizer - Diazo or SBQ
Emulsion solids content
Emulsion viscosity - resistance to flow
Emulsion color
Emulsion age
Mesh count/color
Every emulsion has a different speed
Exact coating thickness
Coating trough lip
Trough Full or not, when you coat
Speed of stroke
Number of coats - Wet on Wet plus Face coats
The amount of moisture left in the coating.
Electrical power variations
The lamp type
The lamp power - Electrical watts in, then UV-A output
The age of the lamp
The UV-A energy output range
The lamp distance to stencil
The glass type in your vacuum frame
Is there a vacuum?
The color of the vacuum blanket
 

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As a screenmaker, your first job is to harden the stencil so it doesn't dissolve with water. UV energy needs to move all the way through the stencil to the back to completely harden the stencil.


I want you to put a Stouffer 21 Step Transmission Scale on every screen you ever make for the rest of your life. Expose so you get a solid step 7. You get visual feedback that is the best monitor I know.

They only cost US$6 to US$12 depending on where you buy and properly used, it should last a lifetime.

Then you need to calibrate your designs so that fine lines don't get choked because UV energy can bend and scatter in the stencil making the small openings - smaller.

It may be that you have to make 0.020" lines 0.030" in your computer, so that they finally print at 0.020".

Exposure FAQ of Screen Making Products
i hope i dint sound too dence, but could you please in the most simplelest terms how to use the the 21 step transmission. please if you could step by lil step, i have one, thanks so much, maybe if you know of a vid, that would be great too
 

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lol im not, thats the prob. i do have Stouffer 21 Step Transmission Scale , im using diazo dual cure emulsion, (pink) 110 screen white mess, with 25 x 36 exsposer unit .the exposer unit has a timer on it aswell .with no lid. using a foam pad with a board on top of that with a weight on top of that, i dont know how to go about using the scale, do i have to waste a coulple of screens to find out my optinum exposer times, or can a burn a image during the prosses,
 

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Stouffer instructions link

lol im not, thats the prob.

i do have Stouffer 21 Step Transmission Scale ,

im using diazo dual cure emulsion, (pink) 110 screen white mess, with 25 x 36 exsposer unit .the exposer unit has a timer on it aswell .with no lid. using a foam pad with a board on top of that with a weight on top of that,

i dont know how to go about using the scale, do i have to waste a coulple of screens to find out my optinum exposer times, or can a burn a image during the prosses,
The emulsion, mesh count, lamp, etc. don't matter.

Tape the Stouffer scale on the stencil of every screen you expose for the rest of your life.

The link to instructions is in every quoted post in this thread.

|
V
Exposure FAQ Screen Making Products how to measure exposure
 
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hey rich, i hate to admit it, but i found out what i was doing wrong, i was putting my film on the inside of the screen, lol wow, lmao. anyway when i relized what i was doing and corrected my self, and put my film on the print side, all is well, 4:30 was good for me to expose,. thanks for all ya info.
 

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How does one "harden a stencil"?

how does one "harden a stencil"?
Emulsion is basically a poly-resin glue like Elmer's Glue except, when it dries, it will still dissolve with water.

When sensitizer is added, it reacts and joins with molecules in the resins when bombarded with UV-A energy and cross-links the emulsion components in the mesh so it won't dissolve with water.

Insoluble.

Later in the process, stencil remover chemicals can break the cross-links that prevented the emulsion from dissolving and the mesh can be reclaimed.

Most lamps used in home-made sources are low in UV energy output, so exposure needed to completely cure the entire thickness of stencil can take much longer than commercial units. Speed costs money. How fast do you want to go?

Energy needed to expose is like filling a bucket with water. It takes longer with a medicine dropper, but eventually you can fill the bucket as full as a fire hose. The time is relative.
 
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Thank you. Your explanation of the exposure process had been thoroughly helpful. I have tried about 14 times now to make a screen (stencil) and have succeeded only once. The primary issue i have now is with my image (ink toner on film).

It appears to be rubbing off due to mishandling and my last exposure was complicated by light getting through the image. I though that when you said harden the stencil you meant something about hardening the ink on the film. (i understand now).
 

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i found out what i was doing wrong, i was putting my film on the inside of the screen, lol wow, lmao. anyway when i relized what i was doing and corrected my self, and put my film on the print side, all is well, 4:30 was good for me to expose,. thanks for all ya info.
1)does that really matter??
2)4:30?? how many Ws??
3) hey im using textile dw emulsion (used to be purple now its brown(cause of the sentitizer)) with 360w how much time should expose for??
my remover didn't work on the first one this is my forth try exposing and removing obviously I printed as well and nothing..here are the images of what it looks now ...can I print like this ??? I used bleach and other things to clean it. I once clean it with bleach and then did the whole process but I exposed in the back side of the screen. was that the problem..or what??
img 1)
https://mail-attachment.googleuserc...809&sads=T8Ne_1gZiGyxnjGserAt7WIgGOU&sadssc=1

img2)
https://mail-attachment.googleuserc...343804811811&sads=GoKiq8xYzyPi8Tct943fJVha73Q

img 3)
https://mail-attachment.googleuserc...343804848685&sads=kempyOw_JXruBYP7epQ_FfWk-pE

img 4)
https://mail-attachment.googleuserc...343804888543&sads=JgxLLPgyetWioQueSonNXIx8uOc

ps. the screen was brown with my design not trasnparent but semi


thank you for your help!!
 

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1)does that really matter??

2)4:30?? how many Ws??

3) hey im using textile dw emulsion (used to be purple now its brown(cause of the sentitizer)) with 360w how much time should expose for??

my remover didn't work on the first one this is my forth try exposing and removing obviously I printed as well and nothing..here are the images of what it looks now ...can I print like this ???

I used bleach and other things to clean it. I once clean it with bleach and then did the whole process but I exposed in the back side of the screen. was that the problem..or what??

ps. the screen was brown with my design not trasnparent but semi
1) Yes, it matters where you put the positive. It's job is to block UV energy from reacting with the sensitizer and changing the stencil from something that dissolves with water INTO something that won't dissolve with water -ESPECIALLY with water-based ink. If you don't completely cure the inside of the stencil, the raw stencil will breakdown with the combination of the water & ereaser rubbing of the blade.

2) 4:30 seconds for a diazo stencil is what I would expect from a commercial screen exposing 1K (1000 single lamp), unit. 40 watt BL lamps at least 12 minutes.

3) 360 watts? I'm guessing you are adding up multiple fluorescent lamps to come up with 360. Even commercial, 40 watt BL lamps only output 9 watts of UV energy at 5 inches

Emulsion
The two parts that make "emulsion" are poly-vinyl acetate (white glue, like Elmers), surrounded by poly-vinyl alcohol that the sensitizer joins with.

Under-exposed stencils means some of the stencil you want to resist water - doesn't. The PVAlcohol dissolves on some molecules revealing PVAcetate that then sticks to your mesh LIKE GLUE. Stencil remover won't release it.

Bleach is a very weak method of breaking the cross-links formed by exposure to make a stencil insoluble. No cross-links because of under exposure, no mesh reclaim - bleach or commercial sodium meta periodate (SMP).

I've got about 20 posts on bleach
http://www.t-shirtforums.com/search.php?searchid=4079111
 

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1) ? huuh lool can you explain it like if u were explaing it to a ten year old :$
2) ahh so if its 300w normal lamps like the ones for the office or hallway in your home. then it would be 40w=12
300/40=7.5
7.5x12=90m
90m=1hr 30m exposure time yes??
3) yes different lamps to make 360 or 300 depending if i use one lamp or not
https://mail-attachment.googleuserc...343955414341&sads=5GlBdRH2S_9rCSgMHMfuOjOkJuk

about 10 or 12 inches

emulsion: ohh nice i did smell the glue smell hahaha

oh so i have experienced some underexposure( i started with 16 minutes the 19 and then 32 and it turned yellow but still lost details, so im guessing with my math above it would be 1hr and 30 minutes of exposing eh? )

"The PVAlcohol dissolves on some molecules revealing PVAcetate that then sticks to your mesh LIKE GLUE. Stencil remover won't release it. " HUH??

"Bleach is a very weak method of breaking the cross-links formed by exposure to make a stencil insoluble." is there anything strong enoough??

"No cross-links because of under exposure, no mesh reclaim " but after my first exposure i printed it on a shirt and then i washed it but the emulsion didnt take out very good with the remover and i then washed it with water...soo idnt knw if its creossed linked :S
those pictures were taken yesterday i washed it today with bleach and its much cleaner then yesterday but still not white enough and unlike the cleaning videos when washed with water it doesnt remove :S [media]http://www.youtube.com/watch?v=hZJu-0a0Dl4[/media]

(i dint use pure bleach aas she did today and i did it exactly like she did) (yesterday i let the mixed bleach (water) to stay there to about 5,8,10 minutes each)

" bleach or commercial sodium meta periodate (SMP)." huh?? lol srry :s
 

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Your Google attachments don't work.
 

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oh so i have experienced some underexposure( i started with 16 minutes the 19 and then 32 and it turned yellow but still lost details, so im guessing with my math above it would be 1hr and 30 minutes of exposing eh? )
The simplest way to understand your exposure volume is to measure it rather than keep guessing.

A manual, stepped exposure test looking for the amount of exposure that no longer gets a diazo color change reaction of the stencil will tell you your maximum exposure time.

Because of the physics Inverse Square Law, simple math won't get you an answer.

10-12 inches from glass defeats almost all the light energy of your fluorescent lamps. The industry standard is 4 inches from glass, on 4 inch centers.

Office or hallway fluorescent lamps are designed for reading, not exposing UV sensitive stencils. Look at the model or style of your lamps. If they're NOT BL, you only have a minuscule amount of UV energy and hardly any penetration power need to get to the inside of the stencil. If you can see the light or you feel infra-red heat from a lamp, that energy means nothing to UV sensitive stencils.

"The PVAlcohol dissolves on some molecules revealing PVAcetate that then sticks to your mesh LIKE GLUE. Stencil remover won't release it.

" HUH??
Perhaps you could identify what is confusing you rather than just writing "HUH?" As a teacher, I need to understand where the gap is between what I wrote and what you understand.

Underexposed means the outer covering of PVAlcohol surrounding the PVAcetate (glue), dissolves on some molecules during development and glues the stencil to the mesh and now that it's glued to the mesh, stencil remover or bleach won't defeat the glue.

"Bleach is a very weak method of breaking the cross-links formed by exposure to make a stencil insoluble." is there anything strong enoough??


"No cross-links because of under exposure, no mesh reclaim "
Under exposed means NO CROSS-LINKS for the stencil remover to break.

If your bleach technique works, you should keep using it. If it doesn't work, I suggest using commercial stencil remover with the active ingredient sodium meta periodate (SMP)

(i dint use pure bleach aas she did today and i did it exactly like she did) (yesterday i let the mixed bleach (water) to stay there to about 5,8,10 minutes each)

" bleach or commercial sodium meta periodate (SMP)."

huh??
I posted a link, to a T-Shirts Forum search with more than 20 results of homework posts by me about the inferiority of bleach, compared to commercial stencil remover sodium meta periodate (SMP).

http://www.t-shirtforums.com/screen...ting/screen-printing/search....archid=4079111
 
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