Nobody can tell you how long with the information you listed.
What emulsion are you using? Solvent resistant diazo sensitized emulsion takes 5 times longer to HARDEN than plastisol style SBQ emulsions.
What is the distance of your screen to the lamp? Invisible UV energy degrades with distance.
When you are tired of guessing, purchase a Stouffer 21 Step Sensitivity Guide US$8.00 to US$12.00 depending on where you buy it. It will give you visual feedback and should be on every screen your make for the rest of your life.
It is a 5.5" film positive that is opaque on one end and clear at the other, with 21 measured steps in between.
The 21 steps, simulate 21 different exposures with one exposure. You get visual feedback so you can make clear judgements about exposure without guessing.
When you develop the stencil, areas that didn’t get exposed will dissolve with water and go down the drain like the inside of the screen. You want a minimum of a Solid Step 7 that survives and holds in the mesh. More exposure will make your stencil more durable and less will make the stencil less durable
A forum community dedicated to T-shirt merchants, professionals and enthusiasts. Come join the discussion about graphics, commerce, dyes, prints, collections, guides, displays, styles, scales, equipment, accessories, reviews, classifieds, and more!