T-Shirt Forums banner
1 - 18 of 18 Posts

·
Registered
Joined
·
257 Posts
Hi,

To expose a screen with sun light you will need some special supplies:

1. 2 or 3 inch thick foam pad that fits inside your screen
2. Black cloth to cover your foam pad
3. A piece of glass the size of your vellum or film positive
4. Vellum or film positive with an image on it
5. Tape for vellum or film positive

Do this step inside or out of UV light.

Lay the screen over the foam pad with the cloth fabric side up (this prevents the light from scattering and exposing the back side of the screen). Place the vellum or the film positive on the screen so that is centered and square with the frame, it must be wrong reading as you look down at it. Tape it down and lay the glass over it.

If the sun is out, take the screen outside and expose it for 30 seconds, you might have to experiment with this time. After you do this a few times you will know. If it is cloudy or early or late in the day, you will have to expose it for a longer period. The ideal time is noon when the sun is as directly overhead as it gets.

After exposure take the screen to your washout sink and rinse it off with water as you would any other exposed screen.

I hope this helps and Good Luck on your exposures.

Bill M :)
 

·
Registered
Joined
·
1,810 Posts
whats the best way to set it up, its soo beautiful out and sunny
Remember, every day, every hour and every weather condition will give you different UV exposure conditions.

Please invest $10 in a 10 or 21 step transmission gray scale and put it on EVERY screen you expose.

If step 7 remains in the mesh during washout, you have a well exposed screen and you have a benchmark to compare other screens to. If step 8 remains in the screen, you have more exposure than you need. If the image prints OK, and fine lines don't close up because of light undercutting - OK.

But if you only hold a step 6, you should expose longer. You get instant feedback on the amount of exposure.


When I took 20' flag screens into the alley because they didn't fit in the exposure unit, I attached the positive with Wisconsin's own water soluble KY Jelly. An ultra thin layer held the positive in intimate contact with the stencil and I rolled the positive in place with a 'brayer'. The KY dissolved and went down the drain with the unexposed stencil during wash-out. The positive was easy to clean.

Paper positives actually become more transparent as the KY is absorbed by the paper.
=======================
20' flag screens are very big. You haven't lived until you go to the pharmacy and ask the clerk in a low voice, "Don't you have a larger container." and the clerk shouts to the back room, "Don't we carry a 5 pound jar of KY jelly?".
 
  • Like
Reactions: thutch15

·
Registered
Joined
·
164 Posts
Screenprint Answers by Bill Hood
for a natural sun exposure unit only 20 sec(summer) to harden 40 sec winter
There are instructions on using a Compression Exposure Unit at Screenprint Answers (Screenprint Answers by Bill Hood) but in brief they are:
1. Choose a place indoors, away from direct sunlight to prepare your exposure unit. Place a sheet of foam cut to fit into the screen on a table and cover it with the piece of black cloth.
2. Place the screenprint frame - coated with emulsion that’s dried – over the of the foam and cloth squeegee side down with the bottom of the screen facing upward. Because the emulsion is ‘slow’ you can do this indoors if you act quickly.
3. Place the film positive to be exposed on the emulsion surface “wrong reading” (i.e. backwards) in the center of the screen. Assure that the image is square with the frame by using a T-square or ruler to measure. Once in place, tape it down with the Scotch Brand 810 Magic Tape.
4. Place a clean plate glass (do not use tempered glass as it will inhibit the UV light) over the art, sandwiching the art between the glass and the screenprint mesh.
5. Expose the emulsion to UV energy from above. This unit can be carried out into the sun for 20 seconds on a bright day to expose the emulsion. Or you can use a single point light source situated above the unit. The distance from lamp to screen should be equal to the diagonal of the frame.
6. You can use the inexpensive Step Wedge Exposure Calculator (Products and Services for Screenprinters) for determining your exposure times.
will make sharper images and finer lines
 

·
Registered
Joined
·
3 Posts
I am a newbie to both this forum and to screen printing in general. I have tried to expose Diazo photo emulsion 3 times now, and today I exposed it, in 5 minute increments, from 10 to 90 minutes. I did not get a single image of the numbers. There was no image burned in at all, nothing was visible. I am trying to limit my investment in this adventure right now if I can so I don't want to buy anything else like lights for a while if I can. Money is a little hard to come by, but if I have to I will. I have seen alot of people with pics and video showing that it can be done, I just haven't been able to do it. I have exposed screens for much less time in the past. I believe I started at about a minute or 2, then 20 minutes then today's experiment. I have tried a total of three times with no results.

Help! I have been at this forever and am really getting frustrated, and it is frustrating hubby too. he is my business partner and wants result LOL
 

·
Registered
Joined
·
1,358 Posts
I am a newbie to both this forum and to screen printing in general. I have tried to expose Diazo photo emulsion 3 times now, and today I exposed it, in 5 minute increments, from 10 to 90 minutes. I did not get a single image of the numbers. There was no image burned in at all, nothing was visible. I am trying to limit my investment in this adventure right now if I can so I don't want to buy anything else like lights for a while if I can. Money is a little hard to come by, but if I have to I will. I have seen alot of people with pics and video showing that it can be done, I just haven't been able to do it. I have exposed screens for much less time in the past. I believe I started at about a minute or 2, then 20 minutes then today's experiment. I have tried a total of three times with no results.

Help! I have been at this forever and am really getting frustrated, and it is frustrating hubby too. he is my business partner and wants result LOL
Exposing a screen in the sun takes less than 2 minutes in direct sunlight.
 

·
Registered
Joined
·
3 Posts
I started at 2 minutes on my 1st screen and nothing happened. Then I read more and exposed it longer on the 2nd and 3rd screens, again nothing happened. I will try a short time at midday again but I am getting discouraged with this.
 

·
Registered
Joined
·
63 Posts
some informative tip posted why don't u just buy or borrow a cheap halogen work light.and make a stand. your local hardware should have it. this is the cheapest exposure unit available.and i can be more controlled. u need a dark room. u can you tube search (explore units) spend a hour or two and watch some videos. u might learn some thing.

[media]http://www.youtube.com/watch?v=XL5AW-VVNgo&feature=related[/media]
 

·
Registered
Joined
·
1,810 Posts
I have tried to expose Diazo photo emulsion 3 times now, and today I exposed it, in 5 minute increments, from 10 to 90 minutes.

I did not get a single image of the numbers.

There was no image burned in at all, nothing was visible.

I believe I started at about a minute or 2, then 20 minutes then today's experiment. I have tried a total of three times with no results.
Try to be more specific about "nothing happened". Do you mean no color change, or the entire stencil dissolved with water?

The purpose of exposure
The purpose of UV exposure is to change the stencil from something that will dissolve with water, into something that won't dissolve or breakdown with water. Keep this in mind and your solution is clear.

Exposure is easy. If the image area you blocked from UV exposure doesn't dissolve and holds in the mesh, something cross linked it. Your positive failed you.

If the entire stencil resists dissolving, the sensitizer did it's job and hardened.



Measure Exposure
To measure stencil hardness (resistance to developing or cleanup solvents), I suggest a US$10 Stouffer 21 step gray scale to simulate 21 different exposures. This is a standard photographic darkroom test positive that's been used since the 1930's.

Put it on every screen you expose for the rest of your life.?
http://www.ulano.com/FAQ/FAQexposure.htm#Q1



Positive comparison
Next time you expose any screen, test if your positive completely stops UV energy. Tape a dime (or any thin coin), or a piece of aluminum foil to the outside edge of your stencil. No light will penetrate the dime and that area should wash out like a dream compared to your positive.

 

·
Registered
Joined
·
17 Posts
Mr Greaves is indicating that the difficulty with Sun exposure is this:It is extremely difficult to predict your result. Depending on factors like the time of day, time of the year, cloudiness, etc, you are quite likely to get either under or over exposure using the Sun. This may not be critical for large block images, and sign printers have used the method for years when they need to expose very large screens. But relying on the Sun for multiple exposures throughout the day and using an exposure calculator for each exposure would be far closer to a science project than a production process, particularly if you are trying to hold any sort of fine detail or halftone dots.
You really can't beat a good point light exposure unit for predictability and repeatability, and that's what process control is all about. And without process control, well...it's just a hobby.
 

·
Registered
Joined
·
3 Posts
There was no image visible in the emulsion, just the emulsion. No image was visible after the wash out, just the emulsion as it was applied. The emulsion does change color, but it was all even and level. NO image was visible.

Try to be more specific about "nothing happened". Do you mean no color change, or the entire stencil dissolved with water?

The purpose of exposure
The purpose of UV exposure is to change the stencil from something that will dissolve with water, into something that won't dissolve or breakdown with water. Keep this in mind and your solution is clear.

Exposure is easy. If the image area you blocked from UV exposure doesn't dissolve and holds in the mesh, something cross linked it. Your positive failed you.

If the entire stencil resists dissolving, the sensitizer did it's job and hardened.



Measure Exposure
To measure stencil hardness (resistance to developing or cleanup solvents), I suggest a US$10 Stouffer 21 step gray scale to simulate 21 different exposures. This is a standard photographic darkroom test positive that's been used since the 1930's.

Put it on every screen you expose for the rest of your life.?
http://www.ulano.com/FAQ/FAQexposure.htm#Q1



Positive comparison
Next time you expose any screen, test if your positive completely stops UV energy. Tape a dime (or any thin coin), or a piece of aluminum foil to the outside edge of your stencil. No light will penetrate the dime and that area should wash out like a dream compared to your positive.

 

·
Registered
Joined
·
3 Posts
Your screen was way over exposed. Look at decreasing exposure times. Make sure your film positive was opaque and dark. Mark sure you have good tight contact of that film positive to the screen. And yes, use a 21 step exposure calculator.
 

·
Registered
Joined
·
1,810 Posts
Overexposure, Light Scatter & Undercutting

Your screen was way over exposed.
If the stencil doesn't dissolve, the sensitizer did it's job. You may waste time & electricity, but in this case, I don't think changing exposure time is your first modification. I think it's Positive Failure and you should compare the positive to a dime or aluminium foil that are known UV energy stoppers.

Exposure
Complete exposure means that UV energy has completely moved through the whole stencil thickness and crosslinked all the sensitizer.

Any less is Underexposure, which is bad for stencil resistance & durability because any un-crosslinked sensitizer is a stencil weakness and makes reclaiming harder.

There is nothing wrong with exposing for longer than necessary - you just waste electricity and time when the stencil no longer changes.

Overexposure?
This is not like overcooked food that dries out, or UV sun burned skin at the beach. Like cured plastisol or concrete - you can't over cure a stencil. No real harm comes from exposing a stencil after all the sensitizer is cross-linked, you're just wasting time and electricity.

Light Scatter & Undercutting
What I think you're trying to warn screen makers about is Light Scatter & Undercutting.

Exposure, all exposure, strikes most of the stencil at an angle.

This increases the pinball like bouncing that happens inside the stencil -Light Scatter and the angle defines Undercutting that causes detail to shrink on the mesh, with eventual loss of parts of the image altogether, especially with fine lines & halftones.
 
1 - 18 of 18 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top