Base for starting exposure test (yeah another one)

[Gilligan]

Alright... any last minute advice?  In about an hour I'm gonna give this a whirl.

I'm using this wedge test:
http://www.smrsoftware.com/vellumexposure.php

If I do 30 second intervals from 30 to 4 mins as Andy suggested will that give me a rough enough estimate?  I really got one shot at this as I only coated 3 screens and I need two for the job.

[tpitman]

The cheap Stouffer scale is like a neutral-density filter that has 21 steps, and you adjust your exposure to get a solid step 7 on the scale. It also comes with the formula for calculating time adjustments to hit that step 7 after your first test. It also comes in handy to throw on a screen periodically to gauge the declining strength of your light source. Some recommend using it on every exposure. It's pretty small, so you can just do a small swipe of emulsion on your screen to perform the test instead of testing fully-coated screens.
Just sayin' . . .

[Frog]

My advice actually called for two volunteer screens for this suicide mission. The first being a little rough and the second, really zeroing in with 10 or 15 second steps for fine tuning.
You are flirting with "settling"

Tom, your suggestion is fine, but we have already established that he is using a manual test with his own film, and should learn a lot from it.

[Gilligan]

Andy, I totally understand what you are saying... I'm just kind of under the gun and want to get this spot job done and out of the way.  The more confident I am at this entire process the more likely I am to do some more testing.

I also have NO darkroom or REAL washout booth setup.  It s a good thing it is night time as it makes for easier washout.   Once everything is PROPERLY setup then it will also be a LOT easier to test everything out.

So... here is what I got from my first run.  Looks like about 2.5 minutes was getting me a pretty decent 1pt line.  Nothing got me a .5pt line and at 2 minutes I lost some entire grid blocks from the 2pt grid (this COULD be because of an improperly prepared screen too.)  EVERYTHING at 2pt exposed well, even at 4 mins.  I guess my vacuum storage back system worked out ok in the end.

Is .5pt really reasonable on most setups?  Or is that reserved for really good single point vacuum lid (nuarc) setups?

I'll take some pics later and post them.

[Frog]

1/2 point should hold with even most decent compression type set-ups with a single point light (and a properly prepared screen). You may even have better detail ability with your space bag.
I have never needed an outline smaller than that, and would never even count on holding a one point reversed line.
Now, did you also get to see the gradual change from under exposed to good to over exposed? That's the added benefit to this, having it all laid out in front of you.

Make sure that you document this and use it as a stepping off point when changing coating techniques, emulsions, or different colors or mesh counts.

[Gilligan]

Ok... so here are the pics.

First off... 2:1 rounded edge is SO much better (thicker) than 1:1 sharp edge.  Wow... I mean, I can FEEL the EOM vs the ones my buddy's guy did for me.  Just Wow!

Ok, so First pic is wide shot of the Wedge test.  Oh, and I guess I really need to note that I really F'd it up.  I put the film on backwards LOL  in the dark I guess I missed that.   So that is probably why my 1pt and .5 pt didn't hold very well... it was probably severely undercut through the film! LOL

2nd pic is a close up of the wedge test.  Obviouysly 3,4 and 5... which were 1.5mins 2mins and 2.5mins.

3rd is my screen that I shot.  I did it for 2.75 mins... actually I did that one for almost 3 mins because I forgot to pull off a part of my shutter so it was only getting like 20% for the first 20 seconds.

4th is the close up of the smallest text.  I'd say that text is comprised of CLOSE to 1pt lines.  SO that's pretty damn good if I do say so myself.


Overall VERY pleased and I bet my next test will be awesome when I actually put the film on correctly. LOL  I only noticed that I did this when I saw the ink residue on the vacuum bag as I shot the actual screen after the test.  Felt pretty smart.  But felt pretty confident on pushing the exposure past the 2.5 by the extra 15 seconds.  Especially on the first screen (not pictured) as it was MUCH larger spaces.

[Gilligan]

LOL... so I realized today that I was COMPLETELY doing the step test wrong, but doing the math right... which was giving me completely the wrong answer.

I was doing some 200 mesh stuff for the first time and figured I needed to redo my test anyway to fine tune it as well as get the times for the 200 mesh.

So I cover everything but the 8 and start exposing.  Wait till 2mins and then start moving it every 15 seconds.  But half way through I realize that was doing it all wrong and then at the end I would have a 15 second exposure and then +15 seconds on each one up till the 8th one which would be like 4 mins.

BAAAHHH... so last time I did the same thing... thinking I needed 2.5 mins well... obviously I was WAY wrong and was WAY over exposing the screens that I did.  Surprisingly that small "E" still worked out (guess that vacuum bag REALLY worked well).

So anyway... I realized today that 45 seconds to 1min was good enough... closer to 45 seconds as 1 min started closing up the .5 pt line... probably could have forced the line with a pressure washer but obviously that's not doing it right.

Guess I need to do it again and time it correctly.  I'll just start at 30 seconds (I guess) and start adding up 10 seconds at a time. *shrug*

1st pic is full shot, 2nd one is 2 through 6. (30 seconds, 45 seconds, 1min, 1:15, 1:30).

[Evo]

Just seems pricey... I'm sure it's good I just wish there was a PDF that one could print and accomplish the same results.

Yeah, I'm cheap, what can I say!

Whan you get a real live working exposure unit, call a Ulano rep and ask for a sample of emulsion and an exposure calc kit. It will come in handy.


If you want a not-so-fussy way of calculating the exposure with the light source you have, buy a small can of 3m Artist's Adhesive spray. It's a removable, positionable adhesive.


Print out  a film with some detail lines, dots, text and some thick lines and shapes. Maybe some halftones too.

Spray a light coat of the adhesive on the film, wait a half a minute, then stick it straight to the emulsion. This will give you the contact of glass/vacuum without having to cycle the vacuum off and on and you won't knock the film out of position on the screen when blocking and unblocking the light. (you can even burn a screen in the sun in a pinch this way...)

Do your step wedge. Try 10-15 second increments and do several above and below your estimated exposure time. Most of the step tests I ever did were about 10 exposures total.

Now take the one exposure that looks the MOST exposed and still holds the finest lines and detail, and do another test with 5 second increments above and below. Again, look for the MOST exposed (as in the one with the emulsion that is exposed all the way through) that still holds the detail without pinching dots and lines.

Now you have your first screen and a starting point.

Now do this once more for each mesh count and/or mesh color.

[Evo]

I also have NO darkroom or REAL washout booth setup.  It s a good thing it is night time as it makes for easier washout.   Once everything is PROPERLY setup then it will also be a LOT easier to test everything out.

Remember it's screen printing. First things first: make sure you can make good screens. Your printing will never be better than the stencils you can produce.

Money isn't an issue btw. You just need a clean space that can be made dark and is easy to mop.

[Gilligan]

I've been doing ok so far Evo.  Even coating I haven't made too much of a mess.

Exposing wise I do have the vacuum bag and they are working very well... so far it's holding it's vacuum for a long time and it's very tight.  No chance of it moving and it's very tight to the screen.  I have a hard time getting the little kinks out it's so tight of a vacuum, and that closing the valve and removing the vacuum unit.

The test sheet I'm using (pictured) has some .5pt stuff which to me looks pretty fine but I'm pretty ignorant on these things.

[Gilligan]

Ok... now that I re-evaluate my first test I realized I did calculate it right.  I just screwed up my second one.

So this brings me to a question.  Do LOWER mesh counts result in LONGER exposure times due to essentially a thicker coat?

I'm completely talking out of my arse here because I of course don't know... I did change the setup completely so the distance might have been less (but if it is, we are talking about 1-2 inches out of 30 inches.)

Also if anything I THOUGHT I put more emulsion on.  With the 158's I did 2:1 with the 200's I did 3:1 (both rounded edge).

Either way that seems like a large difference in time 2.5 mins down to 50 seconds.  Even if both 2 inches closer and thinner emulsion (though more passes) that seems like too large of a difference.

[Evo]

Ok... now that I re-evaluate my first test I realized I did calculate it right.  I just screwed up my second one.

So this brings me to a question.  Do LOWER mesh counts result in LONGER exposure times due to essentially a thicker coat?

I'm completely talking out of my arse here because I of course don't know... I did change the setup completely so the distance might have been less (but if it is, we are talking about 1-2 inches out of 30 inches.)

Also if anything I THOUGHT I put more emulsion on.  With the 158's I did 2:1 with the 200's I did 3:1 (both rounded edge).

Either way that seems like a large difference in time 2.5 mins down to 50 seconds.  Even if both 2 inches closer and thinner emulsion (though more passes) that seems like too large of a difference.

Yes, the coarser mesh typically will have a thicker filament which equals a thicker mesh which will have more void in the open areas which means a much thicker stencil. Thicker stencil means longer exposures.

Keep in mind also that amber/yellow mesh will require slightly longer exposure times for a given mesh count as well. The yellow dye inhibits the UV energy from creeping along the filaments and causing undercutting and loss of detail. The trade off is longer exposure.

This is why in the above post I suggested getting a very narrowed down exposure for one mesh count, then follow the exact same exposure calculation procedure for each mesh count you use.

The light units required for the range of mesh counts I use ranges from 125 to over 200. I also use 3 different kinds of emulsion, polyester and nylon mesh,  and on the coarser mesh screens I may do additional coats on the print side when a thick ink film is desired. All this means test, test and test again, MAKE A CHART and hang it on the exposure area wall.

Also, it's a good idea to standardize your coating procedure, (example 1+2 on all screens) that way you don't need to do an exposure for each mesh count AND coating method combination.

[Evo]

By the way, if the testing seems like it will take forever, it doesn't. You can do it while dealing with other chores around the shop. All the exposure test screens will reclaim super easy as they won't have any ink muck to deal with.

On the other hand, dealing with bad exposures wastes a ton of time and money. Dial it all in from the start and the rest of your screen making becomes a cakewalk.

[Gilligan]

Absolutely... I definitely want to get the process down better and more accurately.

I lost a little detail in the last design I did (granted it was a distressed thing so only I can tell)... but it was odd... lost some detail here because too much emulsion washed away but only an inch away the opposite happened and I lost detail because the emulsion didn't wash away.

[Denis Kolar]

Absolutely... I definitely want to get the process down better and more accurately.

I lost a little detail in the last design I did (granted it was a distressed thing so only I can tell)... but it was odd... lost some detail here because too much emulsion washed away but only an inch away the opposite happened and I lost detail because the emulsion didn't wash away.

Could it be uneven coating?
I remember my first few coated screens LOL