If I’m understanding this correctly, your process for exposing screens hasn’t changed but you’re not getting the results you normally get.
Some thoughts:
Even though a household bulb seems to have been working for you in the past, it’s not the ideal exposure option. Just spitballing here, but household bulbs have varying lighting options, meaning some incandescent bulbs filter light differently and it’s possible you’re not getting optimal lighting for exposure. You indicated that your process is the same so I’m assuming your bulb has not changed, either. This may not be your problem but I’d be interested to see a photo of your exposure setup - there may be a thing or three you could do to improve exposure.
It’s also possible that the 12-15 minutes you say you’re exposing is too much time. Maybe you’re unintentionally over-exposing, which would cause your screen to be difficult to wash out. If you’ve never tried an exposure calculator to be absolutely sure that you’re exposing for the correct amount of time, you really should. After having used an exposure calculator at least you’ll always be confident in knowing your screens are adequately exposed.
Emulsion thickness matters, and the lower the mesh count is on your screen, the thicker your emulsion coating will be and the longer you’ll need to expose.
The screen in the picture looks like it has the ink residue from your previous print job still in the mesh. You’ll want to do a better job of getting that ink out of your mesh because ink can interfere with the way your new emulsion sticks to your screen. All screens will get stained some but getting all the ink you possibly can out of your screen mesh will also eliminate some exposure doubts.
Again, these are just some thoughts. I may not have really answered your question but you have some food for thought while you try to troubleshoot your exposure problem.
Some thoughts:
Even though a household bulb seems to have been working for you in the past, it’s not the ideal exposure option. Just spitballing here, but household bulbs have varying lighting options, meaning some incandescent bulbs filter light differently and it’s possible you’re not getting optimal lighting for exposure. You indicated that your process is the same so I’m assuming your bulb has not changed, either. This may not be your problem but I’d be interested to see a photo of your exposure setup - there may be a thing or three you could do to improve exposure.
It’s also possible that the 12-15 minutes you say you’re exposing is too much time. Maybe you’re unintentionally over-exposing, which would cause your screen to be difficult to wash out. If you’ve never tried an exposure calculator to be absolutely sure that you’re exposing for the correct amount of time, you really should. After having used an exposure calculator at least you’ll always be confident in knowing your screens are adequately exposed.
Emulsion thickness matters, and the lower the mesh count is on your screen, the thicker your emulsion coating will be and the longer you’ll need to expose.
The screen in the picture looks like it has the ink residue from your previous print job still in the mesh. You’ll want to do a better job of getting that ink out of your mesh because ink can interfere with the way your new emulsion sticks to your screen. All screens will get stained some but getting all the ink you possibly can out of your screen mesh will also eliminate some exposure doubts.
Again, these are just some thoughts. I may not have really answered your question but you have some food for thought while you try to troubleshoot your exposure problem.
