## 3-d shapes for decorations

3-d or three dimensional means a solid shape. This is very satisfying as a decoration for a Christmas tree or elsewhere, but perhaps a little difficult to make. Solid material such as clay or dough is heavy, and needs some skill to produce a good result. It is possible, however, to make a 3-d shape starting from paper or card. You do this by a net. The 3-d shape is taken apart to make a 2-d flat surface. This can be drawn on paper or card, and folded up to reproduce the original shape. Nets for simple shapes such as cubes are part of educational curriculums, so this can be educational as well!

I have written a website on the simple solids, cubes, pyramids, and so on. There is a page for each shape, some information about it, and a net to make the solid. One of the pages describe how you can build up a star from simpler solids. Click here to go to this website.

If you want to make a Christmas decoration, you need to plan it first. I suggest that you chose a shape, and try to make it as a simple shape first, to see what the problems are.

• You must decide what material you are going to use. It's perfectly possible to make a solid shape from paper, as long as the paper is not too thin. But it will be a little tricky to stick together, and fragile once made. It's easy to flattern it! Thin card is better. You can buy this from craft shops. Or you can recycle breakfast cereal packets, or old Christmas cards.
• Draw the net on the paper or card. See below for the net of a cube, or my solids website gives nets for our shapes. You can print these out directly (click with the right hand mouse button on the net and chose Print to do this). That can be used directly for a paper model, or stick it onto the card. But you can also copy this net onto paper or card. This makes it even more of an educational exercise! Get the angles right (use a protractor), and make sure the sides are all the same length. Don't forget to have flaps for sticking the piece together.
• Cut the net out, round the edge, not along internal lines! Crease along internal lines, including the flaps. It is very important that these creases are accurate and sharp. A good technique is to get a ballpoint pen and draw lines (using a ruler) along these internal lines. Do this on the side of the net which will end up inside the shape. (You may need to make one shape first to understand this.) If the ball point doesn't work, so much the better! You don't need the ink - you need the groove that the ballpoint pen leaves. For card, press down quite firmly. You will find that you can crease along the line easily after that. The creases should start to make the paper curl up and the shape appear. Craddle it in your hands, and puch it together to make the shape.
• The gluing stage is tricky. Ideally, you want a good quality hobby glue which will stick quickly, but these tend to be spirit based, and not suitable for children. (In fact, anything that will stick quickly can cause problems with children, as they stick themselves plus anything else to everything else!) Use small amounts of glue - if there isn't enough, you can always use more, but large amounts of slow drying glue is a very bad idea! Start from one flap and work your way round. Neat, accurate gluing is essential. Make sure that edges align, before pressing them toegther. You will really need to press from both sides of the paper or card. This is fine to begin with (stick a finger inside the shape). However the last few flaps will be a problem. You can slide a knitting needle or skewer or screwdriver in through one corner just to have something inside to press against to make the glue stick. Or you could stick all the flaps except those round one face. This will look like a little box with the lid sticking up, especially with a cube. Then glue all the rest of the flaps at once, and stick them all down together, craddling the solid in your hands to press against. Be very careful if the solid is made of paper - it won't take too much pushing! Leave the solid for the glue to dry.
 Tetrahedron Octahedron Dodecahedron Icosahedron Cube Octahedron

Once you can make a solid, then there are various ways to make a decoration.

• You will need to choose a shape. There are several attractive shapes (see above). Click here to find their nets. Most people would think that a cube is a very boring shape, but if you hang it on a string from one corner, it is quite attractive, showing different sides as it turns. A cube octohedron is made from squares and triangles, so quite easy to lay out, and an attractive shape. You can also combine shapes. Sticking pyramids on a base shape to make a star is mentioned above. But you can do something easier, such as a pyramid on a cube to make a (rather geometric) Christmas tree.
• Think about the size. A Christmas tree decoration should be quite small. Your first attempt at a solid (above) should give you some idea how you should change the size. If you already have a good net, you can alter its size in various ways. Save the image onto your computer. You might be able to alter it directly while printing out, or by using Paint software. Or put it into a word processing document, which tend to let you alter the picture by click-and-dragging on a corner.
• It is important that the net is accurate. If you want to draw the net from scratch, then you must be careful. One way is draw round an existing shape. You might already have a plastic square or triangle (or pentagon or hexagon) which you can use as a template, or you can make one out of cardboard. When drawing round shapes, make sure that they are lined out properly. For the large nets, for some shapes such as the icosohedron you might be able to draw straight lines which cover the edges of several sides. This not only saves you work, it makes the whole net more accurate.
• It is probably easier to decorate the shape before cutting it out and sticking it together. On the other hand, you might not know where the decorations should go! You can scribble at random and see what the effect is (see right). Or try a pattern and see how it ends up. Or start with a blank shape, fold it up (without sticking) to see what goes where, then unfold it to decorate it. Decoration could be colouring it with felt-tip pens or paint, or sticking on pictures or shapes or sequins or glittery stuff. Allow everything to dry before cutting the shape out and gluing it together.
• If you are making a star, make the basic shape first and allow it to dry completely before making the points and sticking them on.
• If the glue is causing problems, you could try using sticky tape instead. You can buy brightly coloured Christmas tape which would be a decoration in itself.
• You can have a string or thread to hang the decoration up. The best way to do this is to tape the string inside the shape before gluing the shape together. Make sure that the string exits at a point while gluing the shape together. If the string tends to pull out from the tape, then make a knot in the end of the string of thread before taping it. Also press the tape down firmly on the string or thread, and on the paper either side. It won't matter what it looks like, as all this should end up inside the shape, where you can't see it.
• Some decoration, such as glitter, might be better done once the shape has been glued together. Also, you might prefer decorating it once you can see what the final shape looks like. It will be a little tricky, as the final shape is quite fragile. It can get dented, and the points of a star may fall off. (They can always be stuck back on again.) Allow all gluing to dry before this final decoration. Hold the shape carefully while decorating it. You might get away with paiting if the paint is quite sloppy and you have a gentle touch. But felt-tip pens are not a good idea at this stage, and you risk crumpling the entire shape.

Here is the net for a cube. Click here to find nets for other shapes.