Ink traps are built with Corner Decorations. This page teaches exactly enough of that feature to make traps. The full model is explained in Reusable Corners, Serifs & Caps with Path Decorations.
An ink trap is a small notch cut into a tight joint of a letter, such as the crotch of a V or the apex of an M, to keep the joint from becoming too dark or closing up when the font is printed small. In FontCreator you don't have to carve these notches by hand on every glyph: draw the cut once as a donor glyph, then attach it to every joint that needs it with a Corner Decoration. Edit the donor once, and every trap in the font updates.
Left: the joint fills in at small sizes. Right: the same V with an ink trap — the notch gives the spreading ink extra room, so the printed corner stays open and crisp.
What an ink trap is and why fonts have them
When type is printed very small, especially on absorbent paper or under demanding press conditions, ink can spread beyond the intended outline and make fine details appear heavier. Tight interior corners are particularly vulnerable: where two strokes meet at a narrow angle, the remaining white space can become so small that the joint closes up and turns into a dark blob.
An ink trap compensates for this by deliberately removing material at the joint. The outline may look exaggerated when enlarged on screen, but when printed at the size it was designed for, the spreading ink fills some of that extra space. A well-judged functional trap should therefore be difficult to notice at reading size as the joint simply looks clean.
Classic examples include Matthew Carter's Bell Centennial, designed in the 1970s for AT&T telephone directories printed at small sizes on inexpensive newsprint, and Tobias Frere-Jones's Retina, commissioned by The Wall Street Journal for dense financial tables. Both use pronounced cut-ins at tight joints to compensate for ink spread in demanding small-print conditions.
Functional ink traps are most relevant when a typeface must remain clear at small sizes under reproduction conditions that can close tight details. In output conditions with little ink spread they may be unnecessary. Ink traps can also be used deliberately as a visible stylistic feature in display typefaces. The construction technique is the same; only the purpose and depth are different.
Where ink traps go
Ink traps belong at tight interior joints — places where strokes meet and the remaining white space narrows sharply.
Common candidates include:
- the inside joints of
V,W,MandN, and lowercasevandw - the inner apex of
A - tight crossing or joining areas in letters such as
K,XandY - the closed joint of the digit
4 - in heavy designs, places where a shoulder or bowl joins a stem, such as in
n,m,bandd
Not every one of these needs a trap in every typeface. The actual outline, weight, intended size and printing conditions determine whether compensation is useful.
Outside corners are different. A finish added to an outside corner is normally a serif, spur, notch or another decorative treatment rather than a functional ink trap. FontCreator can create those with the same Corner Decoration mechanism but a different donor.
As a rule of thumb, the tighter the joint and the heavier the weight, the more likely it is to need relief. A light, open design may need no traps at all; a very heavy design may need considerably more space at the same junction.
The tool: a Corner Decoration with a cut-away donor
A Corner Decoration attaches a small designed sub-shape, the donor glyph, to a single on-curve point of an outline.
The host glyph keeps its authored outline. The decoration is applied non-destructively inside FontCreator and becomes ordinary outline geometry when the font is exported.
Many points can reference the same donor. That makes Corner Decorations especially useful for ink traps: define one cut once, then reuse it throughout the font.
For an ink trap, the donor is a cut-away. Instead of adding material to the corner, as a serif donor might, it removes material from the joint.
Step by step: trap the apex of a V
1. Create the donor glyph
Add a new empty glyph to the font and name it:
_corner.InkTrap
This follows FontCreator's _corner.<name> naming convention. When you use Add Corner Component…, the Select Composite Glyph Member dialog is filtered to _corner. by default, making correctly named donors easy to find. You can clear the filter if you want to select another glyph.
Also exclude the donor glyph from the exported font. In the Font Overview, right-click the corner glyph and choose Include in Exports → None. The donor is only used while designing the font and does not need to be included in the final font.
2. Draw the cut
The ink-trap donor must be an open contour. Start at one side of the mouth, draw through the bottom of the cut, and end at the other side. Draw the trap as it should appear at a downward-pointing joint. Do not close the contour. If it is closed, right-click the contour and choose Toggle Open Contour.
A simple donor can be a narrow slit around the glyph origin:
- place the two mouth points slightly above the origin, one on either side
- extend the cut downward beyond the origin
- avoid making the bottom unnecessarily sharp
For a 1000-unit font, mouth points around (−12, 50) and (12, 50) with the bottom around −85 are a reasonable starting shape for experimentation. These values are not a rule — the correct depth depends on the design, weight and intended output size.
Draw the path in the same direction that the host outline travels through the joint: down the entry wall, through the bottom of the cut, and up the exit wall.
3. Add the donor's anchors
Place three anchors on the donor:
origin— at the glyph origin; this represents the corner point that the decoration replacesleft— at the mouth point on the entry sideright— at the mouth point on the exit side
The donor is drawn once. Every trapped joint in the font can reference this same glyph.
4. Select the joint
- Open the
Vin the glyph editor. - Select the single on-curve point at the inside of the apex — the point in the crotch where the two diagonal strokes meet.
- Only that one node should be selected.
Be careful not to select the outer bottom point of the V. The trap belongs in the interior corner.
5. Attach the trap
- From the main menu choose Glyph → Path Decoration → Add Corner Component…
- Select
_corner.InkTrap.
Select the single point inside the joint before adding the Corner Decoration.
With the decoration selected, set its alignment to middle in the Path Decoration controls. Middle alignment follows the joint between the incoming and outgoing strokes and is especially useful when the two sides are not perfectly symmetrical.
The trap is in place. The original host outline remains unchanged underneath the decoration.
6. Repeat and tune
Apply the same donor wherever similar compensation is needed — for example in W, M, N or A.
The process is always the same:
- select one interior corner point
- choose Add Corner Component…
- select
_corner.InkTrap - use middle alignment where appropriate
Then test the result at its intended size.
If the trap needs to be deeper or shallower, edit _corner.InkTrap rather than modifying every decorated glyph. With a trap selected, Glyph → Path Decoration → Go to Source Glyph takes you directly to the donor.
Every joint that references the donor updates automatically.
Tip: Keep the trap design centralized in the donor. That is the main advantage of using a Corner Decoration instead of carving the same notch manually into every glyph.
Watch out: If a trap appears mirrored or faces the wrong way, check the host contour direction. Corner Decorations orient themselves relative to the direction of the path.
To remove a trap, select the decoration and choose:
Glyph → Path Decoration → Remove Decoration
How deep should an ink trap be?
There is no universal depth for an ink trap. It depends on the typeface, the size at which it will be used, and for functional ink traps, the printing process, paper and ink.
A functional ink trap is designed to compensate for what happens during printing, so the final judgment should be made from printed proofs, not from the enlarged outline in the glyph editor.
Print the font at its intended text size using conditions that are reasonably representative of its intended use. Compare trapped and untrapped versions and look at the resulting joint:
- Too shallow: the joint still becomes noticeably dark or begins to close.
- About right: the joint remains clear and balanced without the trap drawing attention to itself.
- Too deep: the notch remains conspicuous in the finished print.
If the typeface is intended for a particular printing process or paper stock, proof it under those conditions whenever possible. An office inkjet or laser printer can still be useful for experimentation, but each produces type differently and neither necessarily predicts the result of commercial offset printing or printing on newsprint.
FontCreator's Test Desktop Font (F5) and Preview panel (F8) are useful for checking the shape at actual text sizes and seeing whether the trap looks visually excessive. They do not simulate ink spread.
For type intended primarily for screens, test it at the actual pixel sizes and on the kinds of displays where it will be used. In that case you are judging rasterization and small-size clarity rather than compensating for physical ink spread.
If a visible ink trap is part of the typeface's design rather than a printing compensation, there is no need for it to disappear at small sizes. Its depth is then a design decision.
Ink traps across weights — and variable fonts
The amount of compensation may change with weight.
As strokes become heavier, tight joints usually contain less white space. A Light design may need little or no compensation, while a Black design may need a considerably deeper cut.
Because the donor is an ordinary glyph in the FontCreator project, it can have different outlines in different masters.
For example:
- Light master → shallow or effectively absent trap
- Regular master → moderate trap
- Black master → deeper trap
The donor then interpolates across the variation space just like the other compatible outlines in the variable font.
Every host glyph that uses _corner.InkTrap follows those changes automatically.
This is one of the major advantages of using a reusable Corner Decoration instead of manually carving traps into every master of every glyph: the design decision remains centralized in one donor.
Exporting: traps become plain outlines
Font formats do not contain a native representation of FontCreator Path Decorations.
When you export the font, FontCreator automatically decomposes the decorations into ordinary outline geometry. The resulting .ttf or .otf therefore needs no special support in the application that uses it.
The trap simply becomes part of the final glyph outline, just as if you had drawn it there manually.
If you want to inspect the decomposed result before export, make a copy and choose:
Glyph → Decompose → Path Decorations
Decomposition is permanent within the project: after decomposition, the geometry is no longer linked to the donor.
Download the example project
Download the sample project and open it in FontCreator to see the technique in practice:
FontCreator-Path-Decorations-Sample.fcp
It contains the _corner.InkTrap donor and its anchors, traps applied to V and W, and the other reusable corner and cap examples from the Path Decorations tutorial.
The M is deliberately left without a trap so you can add one yourself:
- open the
M - select its interior joint
- choose Glyph → Path Decoration → Add Corner Component…
- select
_corner.InkTrap - set the alignment to middle
An optional variable-font sample is also available:
FontCreator-Path-Decorations-Sample-VF.fcp
It contains Light and Black masters so you can see how the donor and its traps change across the weight axis.
Troubleshooting
| Symptom | Likely cause | Fix |
|---|---|---|
| The trap is mirrored or faces the wrong way | The host contour direction is reversed | Correct the contour direction, then check the joint again |
| The trap leans to one side at an asymmetric joint | Alignment is set to in-stroke or out-stroke | Set the decoration alignment to middle |
| Nothing happens when adding the decoration | No single on-curve point is selected | Select exactly one on-curve point at the joint, then add the decoration again |
| The trap appears on the wrong corner | The outer point was selected instead of the interior joint | Remove the decoration, select the point inside the joint, and re-apply it |
| The trap overwhelms the letter | The donor cut is too large | Edit _corner.InkTrap; every use updates automatically |
| The joint still closes in print | The trap does not provide enough relief for the target conditions | Deepen the cut and proof again |
| The notch is visibly distracting at reading size | The trap is too deep for a functional text face | Reduce the cut in the donor |
| The exported font contains only normal outline geometry | Path Decorations are decomposed during export | Expected — the trap becomes part of the final glyph outline |
Frequently asked questions
What is an ink trap?
An ink trap is a deliberate cut or opening at a tight interior joint of a letter. In small-scale printing, the additional white space gives spreading ink room to expand without closing the joint. At the intended reading size, a functional trap should normally be difficult to notice and leave a cleaner letterform.
Do modern fonts still need ink traps?
Traditional ink traps are primarily useful for small print and reproduction conditions where ink spread can close fine details.
In output conditions with little ink spread, pronounced functional traps may be unnecessary. Ink traps can also be used deliberately as a visible stylistic feature in display typefaces.
How do I make an ink trap in FontCreator?
Create a Corner Decoration donor such as _corner.InkTrap, add origin, left and right anchors, then select the single interior corner point of the host glyph and choose:
Glyph → Path Decoration → Add Corner Component…
Select the donor and use middle alignment where appropriate.
Reuse the same donor on every joint that needs the same treatment.
Do ink traps affect spacing or kerning?
Adding a Corner Decoration does not automatically change the glyph's advance width, side-bearing values or kerning data.
The visible outline does change locally, however, so spacing and kerning should still be proofed after adding substantial traps — especially if they are deliberately exaggerated as part of the design.
Do ink traps work in variable fonts?
Yes. Give the donor compatible outlines in the relevant masters — for example, a shallow cut in Light and a deeper one in Black. The donor can then interpolate with the rest of the design, and every joint that references it follows automatically.
How deep should an ink trap be?
There is no fixed value.
Make it deep enough to keep the joint open under the intended conditions, but not so deep that a functional trap remains distracting at normal reading size. Test the finished font at its actual target size and, when the purpose is print compensation, make physical proofs.
What to read next
- Reusable Corners, Serifs & Caps with Path Decorations — the full Corner and Cap Decoration model, including donor anchors, alignment and the Fit option.
