# Cannot Figure Out Correct Exposure Time? (Screen Printing)



## joellep (Jan 15, 2015)

So I have done screen printing before but at uni so we had a proper exposure unit and a lot of help.

I have speedball emulsion stuff (a green colour). And I'm using a S.A.D lamp to expose my screen (which I can't figure out the wattage of but is 10,000 lux and SO bright - like significantly brighter than sunlight!). 

So I read online to only expose screen for 15 mins max - terrible idea that screen barely exposed (and darkened significantly after I removed it from my dark cupboard).

The 2nd time I exposed it for 45 minutes which I figured would actually over expose it, but when I removed it from the cupboard and removed my positives my design didn't wash out (I could see it though) and then almost disappeared when I left my screen out (and exposed further in daylight).

I have my lamp directly above my screen about 10-20cm.


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## dldtg (May 20, 2014)

From what I'm reading S.A.D. lamps have little to no UV lights. Most even advertise 99% UV free or what not. You need a lamp with good UV output to burn screens efficiently.

These linsk may point you in the right direction.

What's the Best Type of Light for an Exposure Unit? - ASPA

How to Build an Exposure Unit - ASPA


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## joellep (Jan 15, 2015)

Thank you for this - I've purchased a lamp, but I actually did another screen before this reply and I did an hour and a half exposure and found it did work to a degree...


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## Ripcord (Sep 2, 2006)

joellep said:


> Thank you for this - I've purchased a lamp, but I actually did another screen before this reply and I did an hour and a half exposure and found it did work to a degree...


That's because all light (well, almost all) contains some UV rays, but most lights don't have enough for screen exposure. An hour and a half is way too long. I expose screens in the sun whenever I can and it takes one minute. On cloudy days I have a homemade exposure unit that uses blacklight fluorescent tubes, and I use a time of 18 minutes for this. I tried setting up a 500W halogen bulb and was disappointed to find that it takes longer than the blacklights. I did an exposure test and came up with 28 minutes (although everything I've read online says 12-15 minutes, that wasn't nearly enough time for the light I used...)

So my recommendation for doing it yourself is the sun, a free source of UV light and the most even light source you're going to get. A lot of guys laugh at me for doing my screens this way, but it truly works extremely well.


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## 343paul (Jan 1, 2012)

Design exposures are the trickiest part in screen printing. Many variables have to be right including:

1. Emulsion that isnt bad
2. Pure Black transparencies
3. Properly prepared screens prior to emulsing (degreasing)
4. Fully dried emulsion for proper cross linking (dry box)
5. Adequate exposure light source
6. EXPOSURE CALCULATOR is key. We test every batch of new emulsion with it


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## 343paul (Jan 1, 2012)

Our little uv box from ryonet exposed screens in 4 mins. Our LED from vastex does it in 20 seconds. Same emulsion diff uv source. Diazo emulsion takes much longer to expose as well. The same emulsion with diazo takes 2 mins in the LED. In the beginning we never used an exposure calc and ruined so many freshly emulsed screens.


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## joellep (Jan 15, 2015)

Hello,
How can I find an exposure calculator? Also the sun is a good idea, but I live in very cloudy/rainy england...

I also saw an exposure strip thing mentioned on this forum but I failed to find it anywhere online which shipped to the UK....


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## 343paul (Jan 1, 2012)

Advancedscreenprintsupply.com has one in the "SCREEN EMULSIONS" section


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## cesarmart34 (Mar 5, 2015)

Ripcord said:


> That's because all light (well, almost all) contains some UV rays, but most lights don't have enough for screen exposure. An hour and a half is way too long. I expose screens in the sun whenever I can and it takes one minute. On cloudy days I have a homemade exposure unit that uses blacklight fluorescent tubes, and I use a time of 18 minutes for this. I tried setting up a 500W halogen bulb and was disappointed to find that it takes longer than the blacklights. I did an exposure test and came up with 28 minutes (although everything I've read online says 12-15 minutes, that wasn't nearly enough time for the light I used...)
> 
> So my recommendation for doing it yourself is the sun, a free source of UV light and the most even light source you're going to get. A lot of guys laugh at me for doing my screens this way, but it truly works extremely well.


serious ****? what stone age exposing unit are you using??? i take 1:50 tops on a bad day


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