How to Separate Stacked Flaps for Sink Folds on Individual Layers

Before pulling the stack apart, compare the current diagram with the next one. Identify the target point, the crease that sets the sink depth, and any instruction to repeat elsewhere. Then trace the target flap from its tip toward its base. Look for the hinge where that flap can turn aside without changing the neighboring structure.

Use a small test movement: lift the target flap slightly while holding the rest of the model loosely. Observe which edges follow it. If an adjacent flap merely rests against it, try turning that neighbor aside. If the paper is joined around a folded edge, treat that connection as part of the structure until the instructions show otherwise.

David Mitchell’s glossary distinguishes a raw edge, which comes from the boundary of the original sheet, from a folded edge, which joins two layers. That distinction helps you locate an opening without mistaking a connected fold for two independent edges. See Glossary of technical terms used on this site.

Make a simple working map before continuing: target flap, neighboring flaps, and shared base. You do not need to mark the paper. The purpose is to know which part you intend to move and which parts should return unchanged after access is restored.

An open sink allows the layers to spread so you can rearrange the point. A closed sink retains a more constrained connection between layers. Mitchell defines this access difference explicitly, while Abrashi Origami School illustrates how separable layers affect the two structures. See Mitchell’s glossary and Abrashi’s sink-fold explanation.

Use that distinction to decide how much separation is appropriate. Opening every available layer is not a universal preparation step: it can change the structure that a closed sink is meant to produce.

What the instructions show	How to approach the stack
Open sink on one identified flap	Move neighboring flaps aside and expose the target’s connected layers.
Closed sink on one identified flap	Isolate the target while preserving the connections required by the diagram.
Sink followed by “repeat behind”	Complete and check the first operation before working the corresponding rear structure.
Several points with no clear layer instruction	Compare the preceding and following drawings before making a new crease.

A designer’s sequence takes precedence over a generic technique. For example, step 14 of Gilad Aharoni’s Cat specifies a closed sink and then a repeat behind. The instruction identifies both the fold type and a separate repetition; it does not ask you to sink the entire stack simultaneously. See the original Cat diagrams.

For an open sink, first return any temporarily lifted flap to its starting position so you can confirm the original stack. Then turn obstructing flaps aside one at a time, using existing folds. Keep track of the order in which you move them so you can reverse those movements afterward.

Hold the model below the working area rather than clamping directly across the sink line. Leave enough freedom for the target flap to open. If access remains poor, partially undo the nearest relevant fold, checking that you can recognize how it closes again. Avoid unfolding distant sections simply to make the model feel looser.

This is a practical access sequence derived from the sources’ distinction between open and closed structures. Its extent depends on the model: there is no fixed number of layers to open or fixed distance to spread them. Your checkpoint is whether the intended crease can move while the surrounding flap arrangement remains understandable.

Locate the sink line from the designer’s reference points. With the intended flap accessible, make the indicated preparatory fold and unfold it. Where the sequence permits, flex that same line in the opposite direction rather than adding a nearby crease by eye.

Origami Resource Center’s sink tutorial begins by folding the indicated line back and forth, then easing the structure open before pushing the point inward. Its example uses a waterbomb base, so the illustrated crease arrangement should not be transferred indiscriminately to another model. See Origami Sink Fold.

Inspect the preparation before collapsing anything. Does the crease reach the intended edges? Have you accidentally included an adjacent flap? Does the target still return to its original position? Correct an unintended shared precrease now, while the stack is accessible, instead of discovering it after the sink has been compressed.

For a diagrammed open sink, use the following working sequence. It adapts the precrease–open–push–compress progression in Origami Resource Center’s tutorial to a model with neighboring flaps that must remain separate.

1. Expose the target. Move obstructing flaps aside along their existing folds.
2. Open its connected layers. Spread the target only enough to see or control the prepared sink boundary.
3. Guide the point inward. Let the surrounding paper change direction along the intended creases as the point enters the model.
4. Pause before flattening. Check that an adjacent flap has not entered the pocket with it.
5. Close the target structure. Bring its layers together along the established folds.
6. Restore neighboring flaps. Reverse your access movements, preserving their original order.

For a closed sink, retain the connections shown by the designer and work within the available opening. Do not substitute the fully opened sequence above simply because it is easier to inspect. Abrashi’s comparison explains that the closed form has intertwined layers and a different crease arrangement from its open example. See What is Origami Sink fold?.

When the whole stack moves, stop before pressing it flat. Return to the last recognizable position and use the following checks. These are troubleshooting suggestions based on the access and crease preparation described above, rather than a model-specific correction sequence.

What you observe	What to check next
Two apparently separate flaps move together	Trace their edges toward the base and look for a shared folded connection.
A neighboring point folds across the sink line	Check whether the preparatory crease accidentally included that flap.
The target opens, but the tip bunches up	Reopen it and inspect the intended crease boundary before pushing again.
The fold looks correct outside but contains an extra flap	Open the unfinished collapse and restore that flap to its previous position.
The structure will not open as expected	Recheck whether the step specifies a closed sink or depends on an earlier layer arrangement.

Also distinguish separation from an unsink. An unsink brings an already recessed point back outward; it is a different operation from moving an overlapping flap aside. Abrashi illustrates this distinction with an example involving a hidden rear layer. Use an unsink only when the sequence requires that structural change. See Abrashi’s unsink explanation.

Compare your result with the next drawing from the same orientation. Check the visible outline, the position of the recessed point, and the order of the surrounding flaps. Gently test whether a flap intended for the next step is still accessible. A matching silhouette alone does not establish that the internal arrangement is correct.

If the instructions repeat the operation on another flap, restore the model first and identify that second target independently. Do not assume that a rear flap opens in exactly the same direction as the front one; follow the diagram’s orientation and connections.

The useful habit is to finish one complete cycle at a time: identify the flap, create access, prepare the sink, collapse it, and restore the stack. Once the first result matches both the diagram and the required layer arrangement, repeat on the next flap with the same checks.

• David Mitchell’s Origami Heaven: Glossary of technical terms used on this site.
• Abrashi Origami School: What is Origami Sink fold?.
• Origami Resource Center: Origami Sink Fold.
• Gilad Aharoni: Cat — original folding diagrams.