Burning High Detail, what do you think?

[brooks]

Hello everybody, thank you for you time in reading this.
I am a newbie to the trade, with big ambitions, little cash . I am using 255 yellow thread count mesh, a pre-sensitized emulsion called Intech HS emulsion. The print will be of a picture in halftone with 65 lpi at 45 degrees, so detail is high. My question is with burning the image, i plan to use pieces from halogen work lights to make one large work light thats houses two 500 watt halogen bulbs, so one housing = 1000watts using 115 volts, standard, the light will be under the image, light going up about 16 inches away from glass. I am wondering what opinions are as to the detail i will achieve using this method.

*note: I am experienced in electrical and carpentry trades, all equipment is safe, the two lights each have their own switch.

Thanks again
-Newbie

[X_Autotype_#1]

Well, for starters I suggest that you learn a little about the sensitivity of the emulsion you are planning to use, then adjust your light source to best suit the conditions of your exposure. You can use 1 million watts of light power, and never get an image if:
- Your light source emits low levels of UV rays (between 440 - 660 nm. is required) - Halogen work lights won't cut this spec.
- Your light source emits higher levels of infra-red (heat) than it does UV, which is exactly the result you will get with halogen work lights. You will likely overheat the stencil during exposure and lock the emulsion into your fabric.
- You have not pre-tested your light source to calibrate the proper exposure time and distance
- You are uncertain of the age of your Pre-sensitized emulsion and/or the storage conditions and it is within it's shelf life.
- You don't carefully and consistently apply a consistent coating layer of emulsion to your fabric, minimizing thick or thin areas (extremely important in halftone printing)

I would suggest that you google the words "correct stencil exposure" and take a look at some of the results. One of them was this link: http://www.poconoscreen.com/tips/photostencil.html which touches on the importance of knowing your light source and testing exposure for best durability and resolution. Note that exposure will vary based on a wide number of issues: mesh count, mesh color, stencil thickness, distance from the light, and so on.

You should at least preform an exposure step-test on a coated screen using the same fabric to get an idea of the resolution and exposure latitude you will have before you shoot your halftone.

Also, call the manufacturer of the emulsion you intend to use and talk to someone in their tech services department. This will save you a lot of time and trouble to know their recommendations. There's a very high number of variables that need to be controlled when considering halftone imaging onto stencil media, and once the image is formed on the stencil, another list of variables applies to printing it.

My advice is to stay away from light sources not specifically suited for UV output. Certainly halogen work lights will not be well suited to halftone printing without a high degree of luck. You'd be better off with a bank of high output fluorescent tubes, but only marginally due to undercutting of the positive. A point light source (single point of light) will always provide better stencil image quality, and metal halide will give you much higher UV output than halogen.

You may also consider having your stencil imaged by an outside source, or a printer that has experience in imaging halftone screens if you want to concentrate your efforts on the printing of the piece (only a thought). But hey, give it a try at least, and let us know how your fare!

Good Luck!!

[jdaniels313]

Man, you couldn't get much better advice than what X Autoype #1 wrote to you! He knows what he's talking about. Only thing I would say is that if your going to start off with those halftones and line counts with the hope of getting anything close to what you want, use an exposure unit made for what your doing; or have some one who has the capabilities shoot the screens for you until you can get squared away on how to expose screens.