Screen Printing Emulsion Troubleshooting Guide

Washout Breakdown

Also called loss of adhesion during development — the emulsion peels, flakes, or washes away during the rinse stage instead of holding to the mesh.

Cause

Contaminated Mesh

Oils, ink residue, or handling contamination prevent the emulsion from bonding to the mesh.

 Fix

Degrease the mesh thoroughly using a dedicated screen degreaser before every coat. Rinse completely and allow to dry before applying emulsion. Shop degreasers �

Cause

Inadequate or Inconsistent Exposure

Underexposed emulsion hasn't fully crosslinked, so it behaves like uncured emulsion and washes away with the image areas.

 Fix

Run a step-wedge exposure calculator to find your correct time. Increase exposure in increments until stencil integrity holds.

Cause

Too Much Water Pressure

High-pressure washout physically dislodges even properly exposed emulsion, especially around fine details and edges.

 Fix

Reduce water pressure and use a gentle spray or flood washout. Work from the print side first, then squeegee side. Allow adequate soak time (30–60 seconds) before rinsing.

Cause

Water Temperature Too Hot

Excessively hot washout water can soften and swell the emulsion, weakening adhesion even on properly exposed screens.

 Fix

Use water between 90–100°F (32–38°C). Avoid hot water — cooler is better than hotter. Room-temperature water works well for most emulsions.

Cause

Screen Not Fully Dry Before Exposure

Residual moisture in the emulsion prevents complete crosslinking, leading to washout failure in image and non-image areas alike.

 Fix

Dry screens horizontally (print side down) in a dark drying cabinet with gentle air circulation. Use a dehumidifier in humid climates. Never rush drying with a heat gun aimed directly at the emulsion.

Cause

Outdated or Pre-Exposed Emulsion

Emulsion past its shelf life, or sensitized emulsion stored too long, may have partially crosslinked in the container — leading to poor adhesion.

 Fix

Check the lot number and manufacture date. Always work under yellow safelight conditions. Store emulsion in a cool, dark location. Diazo-sensitized emulsion should be used within 4–6 weeks of mixing.

Scumming & Haze

A faint film of emulsion residue remains in the open areas of the stencil after washout — visible as a milky haze or slight tint when held up to light. Prints as bleed-through or background toning.

Cause

Incomplete Washout / Underexposure

Underexposed emulsion may appear to wash out, but leaves a thin ghost layer behind. The stencil looks open but scums on press.

 Fix

Increase exposure time and extend washout until all foaming ceases. After rinsing, use a wet-vac or compressed air to remove residual scum from open areas. Inspect on a light table.

Cause

High Humidity in the Screen Room

Excess moisture in the drying or exposure area causes emulsion to absorb ambient humidity, which interferes with proper crosslinking and washout.

 Fix

Keep relative humidity below 50% in the screen making area. Use a dehumidifier, especially during summer months. Dry screens longer in humid conditions.

Cause

Poor Film Positive Contact

Light scatter under the positive artwork causes UV to crosslink emulsion in areas that should remain open, creating a partial cure that shows as haze.

 Fix

Ensure firm, even contact between the film positive and screen surface. Check vacuum frame gaskets and blanket for air leaks. Use a properly dense film positive with OD of 4.0+ in solid areas.

Cause

Pre-Exposure from Ambient Light

Exposure to sunlight, fluorescent lighting, or UV-emitting sources before or during development partially crosslinks the emulsion, creating ghost haze.

 Fix

Work under yellow safelight only. Cover coated screens immediately. Avoid fluorescent lighting — it emits enough UV to affect SBQ photopolymer emulsions. Keep the emulsion pail covered when not in use.

Weak Stencil

The stencil washes out correctly but breaks down prematurely during printing — details erode, edges soften, or the entire stencil degrades after only a few hundred impressions.

Cause

Underexposure

An underexposed stencil appears to hold initially but lacks the crosslink density needed to withstand ink chemistry and squeegee pressure over a run.

 Fix

Significantly increase exposure time. A properly exposed stencil should feel slightly slimy when wet during washout — if it washes very easily, it's likely underexposed. Use a step-wedge calculator to find your ideal exposure.

Cause

Emulsion Coat Too Thin

A thin emulsion deposit doesn't have enough material to build an EOM (emulsion over mesh) sufficient for run-length durability, especially with aggressive inks.

 Fix

Apply 1–2 additional coats on the print side after the initial coat dries. Use the rounded edge of the scoop coater � for higher EOM. Consider switching to a higher-solids emulsion for long runs.

Cause

Wrong Emulsion for the Ink System

A plastisol-optimized emulsion used with water-based or discharge inks can swell and break down quickly due to chemical incompatibility.

 Fix

Match the emulsion to your ink system. For water-based and discharge inks, use a hybrid or dual-cure emulsion rated for water-based chemistry. Hydro X Blue � and CP-Tex � are good options.

Cause

Screen Not Fully Dry Before Exposure

Moisture trapped in the emulsion during exposure interferes with crosslinking, leaving a stencil that looks normal but has reduced durability.

 Fix

Allow complete drying before exposure — this is non-negotiable. Dry horizontally, print side down, in a dark cabinet. Keep the drying area below 50% relative humidity.

Pinholes

Small holes appear in solid areas of the stencil after washout — they print as unwanted dots or specks in your solid fill areas.

Cause

Contaminated or Dirty Mesh

Grease, oils, or fine particulate on the mesh surface prevent emulsion from adhering uniformly, leaving micro voids.

 Fix

Degrease thoroughly before every coat. Handle screens only by the frame — never touch the mesh with bare hands. Shop degreasers �

Cause

Air Bubbles in Emulsion

Vigorous stirring or shaking the emulsion container introduces air that becomes trapped during coating, leaving pinholes when the emulsion cures.

 Fix

Stir emulsion gently rather than shaking. For sensitized emulsions, allow a 30-minute de-gas rest after mixing before coating. Tilt the scoop coater � at a consistent angle during coating to avoid trapping air.

Cause

Dirty or Scratched Film Positive

Dust, fingerprints, or scratches on the film positive block UV light from crosslinking specific areas, creating pinholes that mirror the contamination.

 Fix

Clean film positives before use. Handle by the edges. Inspect prints on a light table before exposing. Replace scratched films — they cost less than reprinting jobs.

Cause

Coating Too Thin for Mesh Count

On coarser mesh counts, a single thin coat of emulsion can't bridge all the mesh openings completely, leaving pinholes at intersections.

 Fix

Apply multiple coats — typically 1+1 (one squeegee side, one print side) as a baseline. For coarser mesh, add a second print-side coat after initial drying. A higher-solids emulsion also helps.

Poor Edge Definition

Edges of the stencil are soft, jagged, or show serrated "sawtooth" patterns instead of clean, sharp lines — especially visible in halftones and fine text.

Cause

Light Scatter (Halation)

UV light scatters sideways through the emulsion, crosslinking areas slightly beyond the edge of the artwork — especially pronounced on clear or white mesh.

 Fix

Switch to a dyed or tinted mesh (yellow or orange) to absorb scatter. Reduce exposure time slightly — halation gets worse with overexposure. Consider a red-pigment emulsion like Hydro X Red �, which is formulated to minimize halation.

Cause

Poor Film-to-Screen Contact

Any gap between the film positive and emulsion surface allows light to scatter under the artwork edges, softening the stencil outline.

 Fix

Ensure the vacuum frame achieves firm, complete contact. Check the blanket and gasket for wear. Place the film emulsion-side-down (emulsion to emulsion) for best contact and sharpest edges.

Cause

Film Positive Not Dense Enough

A film positive with insufficient optical density (OD) allows UV light to bleed through the "black" areas, partially exposing areas that should remain open.

 Fix

Your film positive solid areas should have an OD of 4.0 or higher. Use RIP software and a properly profiled inkjet printer with waterproof inkjet film � for maximum density.

Emulsion Won't Wash Out (Overexposure)

Image areas won't open during washout — the emulsion that should dissolve away is stubbornly holding to the mesh even with extended rinsing.

Cause

Overexposure

Too much UV causes the image-area emulsion to crosslink as well — it can no longer be dissolved during washout.

 Fix

Reduce exposure time by 20–30% and test again. Use a step-wedge calculator — the screen is done at the step where detail holds while image areas still open cleanly.

Cause

Film Positive Too Thin / Low Density

A film positive with weak OD transmits UV through "black" areas, pre-exposing image areas and making them impossible to wash out.

 Fix

Print a denser positive. Test OD with a densitometer — target 4.0+ OD in solid black areas. Double-printing on waterproof film can increase density if your printer isn't achieving adequate black saturation.

Cause

Pre-Exposed or Old Emulsion

Emulsion that has been partially pre-exposed by ambient light, or that is past its shelf life, may have already crosslinked before exposure — leaving no image that can wash out.

 Fix

Discard compromised emulsion. Check lot numbers and manufacture dates. Store emulsion in sealed containers away from any UV-emitting light sources. Fresh emulsion has a noticeably different feel and flow than aged emulsion.