Exposing yourself!

Making Your Artwork Positive.

Having problems getting the right exposure times?

Stencil not washing out?

Stencil too easily losing definition?

Experiencing stencil breakdown whilst printing?

There can be lots of reasons for these problems so we have compiled a simple troubleshooting guide which might help you. It won’t solve every problem but hopefully will point you in the right direction.

Problem	Possible reason and remedy
Image will not washout	Are you using the right level of water pressure? You can use a power hose using light to medium pressure. Normal tap pressure is not enough. If using a pressure washer, is set it to its lowest setting?  How opaque is the film positive? Hold it up to the light. If it is letting light pass through then the emulsion will start to harden making washout difficult. Make sure your film positive printer is set to the darkest settings, you can print out 2 copies of the film positive and stick them together.   You can also use a density spray if printing Film Positives on a laser printer. Has the emulsion gone past its shelf life? Write the date on the label when sensitising – it may save a lot of time and frustration. Screen maybe over exposed. Check your exposure timings – you can use an exposure calculator to determine the right timings / settings for your exposure unit Make sure when drying the screen after coating that you don’t overheat it. Temperature needs to be kept below 40c.
Not all of the image washes out or washes out easily	Screen likely to be under exposed other tell-tale signs include:  If the water runoff is heavily emulsion coloured when washing out and if the emulsion feels slippery and soft. ·         Check your exposure timings – you can use an exposure calculator to determine the right timings / settings for your exposure unit Check for uneven contact between the positive film and screen when exposing. Check the vacuum is working correctly / or glass & weights are in place. Could be uneven coating of emulsion on the screen. Check the tension of the screen – if it is loose you will not get an even coating of emulsion. Maybe time to get the screen re-stretched. Only use light to medium water pressure – too much pressure can remove the artwork inadvertently, resist the temptation to give the artwork a blast with the power washer on anything but light setting. After initially wetting the screen on both sides, washout from the print side only with just a final rinse on the squeegee side. Make sure that the emulsion has been sensitised correctly, the sensitizer powder must be completely dissolved – maybe consider a pre-sensitized emulsion such as Ulano Proclaim EC. Always degrease the screen before coating with emulsion it helps the emulsion adhere to the mesh as well reducing the chance of pinholes and fish eyes
Stencil washed out but ink won’t go through part of it when printing	Check your exposure timings as the screen is likely to be underexposed – you can use an exposure calculator to determine the right timings / settings for your exposure unit  Make sure that the emulsion is thoroughly washed out as the emulsion can run into the stencil on the squeegee side blocking the artwork. Sometimes you can clean it out with a damp cloth (luck is involved – so best to get the exposure timing and washout right) Stencil not dried properly after washing out – you can’t beat a drying cabinet (either manufacturer or homemade). Always inspect the stencil in the light to make sure no moisture remains. Before exposing make sure that the screen is completely dry, the emulsion should be the same ambient temperature of the drying room. If the emulsion is cooler it still has some water content.
Fish Eyes	Normally caused by contamination so make sure you have degreased your screen thoroughly and that your workspace is clean. Also check that the exposure unit glass is clean and that there is no contamination on the film positive.  Check that the coating trough is clean, dust free and that the edge is completely clean (make sure there is no evidence of the old emulsion on the coating trough). When coating the screen, move the trough steadily and with purpose. If you coat too fast the emulsion won’t adhere to the screen correctly. Conversely if you coat too slow and the coating may be too thick. Fish Eyes can also occur during printing if there is an issue with the emulsion e.g. over its shelf life
Pinholes	Similar to Fish Eyes – watch out for contamination on the mesh so make sure you degrease screens.  Dirty glass on the exposure unit is often a culprit, or contaminated film positives. Make sure that there are no air bubbles in the emulsion when coating – when sensitizing emulsion leave it at least for a couple of hours (ideally leave overnight) before using it to allow the air to escape. Don’t coat too fast – allow the emulsion to adhere and fill the mesh aperture

 

Top Tip – Useful tools

Chromaline Exposure Calculator

Chromalie exposure calculator eliminates miscalculated exposure time with three kinds of quality checks. An easy, user friendly tool for the novice and the advanced screen maker.

Designed to help determine correct exposure time, print quality check and halftone tests.

http://www.wickedprintingstuff.com/exposing_equipment_and_digital_screen_makers/accessories_inc_bulbs_foam_and_exposure_calculator_LC241/chromaline_exposure_calculator_P2548.html

 

Maybe the best investment you make!