The Classic Bases

In Origami and Paper Folding 2 you learned to read diagrams and met a handful of simple folds with names, such as the kite fold and the blintz fold. This chapter takes the next step up: the classic bases. A base is a standard sequence of folds that turns a flat square into a shape with a few flaps, and a very large number of models start from one. Learn five bases and you can begin hundreds of models. We finish with the crane, which is built from two of them in a row.

What a Base Is, and Why It Helps

Think of a base as a starting block. A base gives you a fixed number of flaps (the parts that will become wings, legs, heads or petals), and the rest of the model is a matter of shaping those flaps. Because the base is the same every time, folders memorise the base once and then spend their attention on the part that is new. Many books say "begin with a preliminary base" and expect you to know what that means, which is exactly why this chapter exists.

The Five Classic Bases

Here is the family at a glance. Descriptions of the flaps are simplified, and different books count and name things slightly differently (check yours).

Notice that the preliminary base appears in three rows. It is the parent of the family, and it is the one to learn first and learn well.

How Bases Branch

A tree makes the relationships easier to see than a table does. Each line below means "built by adding to":

The Kite Fold, With a Little Geometry

The kite fold is the simplest of these, and it hides a nice piece of arithmetic. Take a square, pre-crease one diagonal, then fold the two edges that meet at one corner in to lie along that diagonal. Each folded edge is as long as the side of the square, so its far end lands on the diagonal. The crease runs from that corner to the opposite edge and cuts the corner angle in half. A right angle halves to 45 degrees at the kite's tip, and each crease makes 22.5 degrees with the diagonal. A tiny script gives the distances for any size of paper:

Output when run:

The "corner" in the output is the corner whose edge folds in. Measure it on your own paper: if the crease lands within a millimetre or two of the printed number, your fold is accurate. The 210 mm row also shows a neat fact: the diagonal of a 210 mm square is 297 mm, the long side of A4, which is no accident, since A4 is designed so that the ratio of its sides is the square root of 2 (check the standard if you want the details).

The Preliminary Base: Learn This One Well

The preliminary base (sometimes called the square base) is built from the pre-creases you already know. It is a small square-looking shape with four flaps, and it collapses almost by itself once the creases are right.

The Crease Map

Here is the paper opened out, with every crease the base needs, as seen from one face. The diagonals are mountain folds and the centre lines are valley folds, which is the key to the collapse.

The rule is the same in every quarter: the lines through the middle that run parallel to the sides go one way, and the diagonals go the other. That alternation, valley then mountain around the centre, is what lets the paper fold flat. We will see in Origami and Paper Folding 9 that this is not luck but a rule.

The Steps

1. Pre-crease the diagonals. Start with a square, coloured side up. Fold it in half corner to corner both ways (triangle folds), creasing firmly each time, and unfold.
2. Turn the paper over. Fold it in half edge to edge in both directions (book folds), crease, and unfold. You should now have all four creases, and the paper will want to make a low pyramid on the table.
3. Make the pyramid. Hold the paper with the centre-line valleys facing you and let the middle rise into a low pyramid: the diagonals ride up as mountains and the centre lines dip as valleys.
4. Bring the corners together. Take the left and right edge midpoints and move them toward each other, folding along the centre lines. The top and bottom edge midpoints fold in on themselves, and the four corners come together at one point.
5. Flatten. Press the whole shape flat. You now have a small diamond (or square, when held a quarter turn) with four flaps, a closed end where the folds meet, and an open end at the bottom where the four original corners of the paper are gathered.

The Bird Base: Adding Petal Folds

The bird base is the preliminary base with its front and back flaps stretched into long points. The move that does it is called a petal fold, and it gets its own proper treatment in Origami and Paper Folding 4. Here you only need to follow it once, and the diagram steps are a good place to practise what you learned in Origami and Paper Folding 2.

1. Set up the base. Hold the preliminary base with the open end pointing down, towards you. Work on the front layer first.
2. Fold the edges in. Fold the two lower edges of the front layer in to the centre line (a kite fold). Fold the top triangle down over them, crease firmly across, then unfold all three folds.
3. Lift and flatten. Lift the bottom corner of the front layer up, and as it rises, the side creases fold in and the top crease acts as a hinge. Flatten it so the layer becomes a long narrow diamond. This is the petal fold.
4. Turn over and repeat. Do the same on the back. The result is the bird base, with a closed point at the top, two narrow flaps at the bottom, and two narrow flaps above them on either side (check how your book orients the base).

The Frog Base in Brief

The frog base starts at the same place as the bird base, the preliminary base, but takes a different turn. Instead of petal folds, you open each of the four flaps and flatten it into a square with a squash fold (also covered in Origami and Paper Folding 4). The result is a base with four wide flaps arranged like a star, much better for models that want broad legs. You will use it in earnest in Origami and Paper Folding 5, so for now it is enough to know it exists and where it comes from.

Your Third Model: The Crane

The crane is the model most people think of first when they hear the word origami. In Japan it is a symbol of long life and good fortune (check), and the story of folding a thousand of them, called senbazuru, is told in many places, usually as a wish for health or peace (check the details if you plan to quote the story). Here is the arithmetic of that thousand, since it makes a good side note:

Output when run:

That is the paper count if you cut from A4 sheets with no clever layout (a 75 mm square is a comfortable size for small cranes). For your first crane, use a 15 cm square so the folds are easy to see.

The Steps

1. Fold the preliminary base. Follow the steps above, and flatten it with the open end pointing down.
2. Fold the bird base. Make the petal fold on the front, turn over, and make it on the back.
3. Narrow the legs. With the two split flaps at the bottom, fold the lower left and lower right edges of the front layer in to the centre line. Turn the model over and do the same on the back. The two bottom flaps are now thin.
4. Fold the legs up (inside reverse folds). Fold the two thin flaps up, one to the left and one to the right, so they point upward at a steep angle. To do it, crease each flap first, open it slightly, and push the point up into the inside of the model so the crease becomes an inside reverse fold (more in Origami and Paper Folding 4). One flap will be the neck, the other the tail.
5. Make the head. On the flap that is the neck, make a small inside reverse fold at its tip, folding the point down. That is the beak and head.
6. Lower the wings. Fold the two upper flaps down on each side so they sit out like wings. Gently pull them apart, and press the body so it puffs out slightly. If you blow into the little hole at the bottom of the body, it will inflate (check the hole is there on your model).

Challenges

Each challenge has a worked solution you can open after you have tried it.

Next, in Origami and Paper Folding 4, we take a close look at the techniques you borrowed in this chapter, reverse folds, squash folds, petal folds and sinks, and fold the flapping bird.