Screen Printing Techniques for Making a Stencil: Paper, Brush, Photo Emulsion
Every print starts with a stencil, and there are three ways to make one.
Paper and cut film. A shape cut from paper, laid under the screen and held by the first pass of ink. It lasts a handful of prints before it softens. Vinyl or cut screen film lasts longer. This is the crudest stencil method and it is still the fastest way to test a composition before committing a screen to it.
Block-out by hand. Screen filler painted directly onto the mesh with a brush, blocking everything that should not print. The mark of the brush survives into the print, which is the reason to do it. Nothing photographic reproduces a loaded brush stroke the way a brush does.
Photo emulsion. The standard method, and the only one that holds fine detail. The screen is coated, dried, exposed through a film positive and washed out. What arrives on the print is exactly what was black on the film, at whatever resolution the mesh can carry.
The photo emulsion route is where most screen printing techniques branch, because once a stencil can be anything a film positive can be, the constraint moves from the mesh to the artwork.
Halftones and Duotones
A stencil is binary, so a continuous gradient has to be faked. The standard fake is the halftone: the image is broken into dots whose size varies with tone, and the eye averages them at reading distance.
Two numbers govern it. The halftone line count has to sit well under the mesh count, or the dots fall between threads and disappear. A rough working rule is a mesh count at least four times the line count: a 45 line-per-inch halftone wants around 200 threads per inch of mesh. The other number is the dot angle, which matters as soon as a second colour is involved, because two dot grids at the same angle produce a moiré pattern instead of a picture.
A duotone takes that further: two halftone screens of the same image at different angles, in two inks, giving a tonal range neither could carry alone. It is a cheap effect in screen printing terms and it looks expensive.
Multi-Colour Screen Printing and Registration
Multi-colour screen printing is where the process gets difficult, and registration is the whole of the difficulty. Every colour after the first has to land in the right relationship with the ones already printed.
The sheet is what gets registered, not the screen. Three stops on the printing bed hold each sheet in the same position, and the screen swings down into the same place. If both are fixed, colour two lands where colour one is. Registration marks on the film positives, small crosses outside the image area, let each screen be aligned to the previous print before the run starts.
Light inks first, dark inks last, and a hair of overlap where two colours meet.
Two habits make multi-colour work survivable. Print light colours first and dark last, so small misalignments hide under the darker ink, never on top of it. And build a trap: let adjacent colours overlap by a fraction of a millimetre instead of meeting exactly, because a perfect butt join shows a white line the moment registration drifts by a hair.
Paper moves. It absorbs water from the ink, expands slightly, and dries back. Over a long run of multi-colour screen printing through a humid week this is a real source of drift, and the answer is to print all of one colour in one session and never across several days.
Split Fountain and Other Things That Break the Rules
A split fountain puts two or more inks side by side on the same screen and lets the squeegee blend them across the image. Every pull shifts the blend slightly, so no two prints in the edition are identical. Commercially that is a defect. In poster and art printing it has been a signature effect since the sixties, and it is the reason a lot of people get interested in screen printing techniques in the first place.
Deliberate misregistration belongs in the same category: printing a colour a few millimetres off and letting the offset read as an effect and not a fault.
Overprinting is the quiet one. Transparent inks laid over each other mix optically on the paper, so two screens can produce three colours, and three screens can produce seven. Planning for it turns a four-screen budget into a much richer print.
What the Mesh Will and Will Not Hold
Every technique above runs into the same ceiling. Fine mesh holds fine detail and passes little ink. Coarse mesh passes a lot of ink and loses anything small. A hairline rule at 305 threads per inch prints; the same rule on textile mesh closes up and disappears.
The practical test is to include a detail strip on the film positive: a few hairlines, some small type, a 5% and a 95% halftone patch. After wash-out, the screen shows what survived before any ink is mixed. It costs nothing, and it settles arguments about whether the artwork or the screen is at fault.
Frequently Asked Questions
Which stencil method is best for detailed artwork?
Photo emulsion. Hand-cut and painted stencils have their own character but cannot hold small type, hairlines or halftone dots.
What mesh count is needed for halftone screen printing techniques?
At least four times the halftone line count. A 45 lpi halftone needs roughly 200 threads per inch; finer halftones need finer mesh and thinner ink.
How do you keep registration accurate across several colours?
Fix the sheet position with stops on the bed, fix the screen position with hinge clamps, align each new screen to a printed sheet using registration marks, and print the whole edition of one colour in a single session.
What is a split fountain print?
Two or more inks loaded side by side on one screen and blended by the squeegee, so the print carries a gradient across it. Each pull differs slightly, which makes every copy in the edition marginally unique.
Why do two halftone colours produce a strange pattern?
Because the dot grids are at the same or a similar angle and interfere. Separating the angles by around 30 degrees removes the moiré.
Can transparent inks be overprinted to make new colours?
Yes, and it is the most economical technique available. Two transparent screens overlapping give a third colour where they cross, so a three-colour budget can produce six or seven visible colours.