Thank you for all the nice comments on my jacket-in-the-making! I think I should stop calling it the 'Tetris-jacket' because although cutting it out required a lot of Tetris-related skills, the end-result should have little or nothing to do with piled-up blocks... Suggestions for a new name are welcome!
Many of you asked questions about sewing with leather. I'm by no means an expert but I have dabbled before and so I will try and answer your questions, as well as give some additional pointers.
1. There are many different kinds of leather, depending on the animal it comes from and the way it has been treated (e.g. suede is just 'brushed' leather...). Suitable leather for clothing is usually lambskin although goat, calf and pig are used as well. Cow skins are much thicker and usually used for upholstering furniture.
It is often easier and much cheaper to find second hand leather garments which you can cut up and re-use. Not to mention that it's more environmentally and animal friendly... Apart from real motorcycle jackets, all leather used in clothes is of the kinds I mentioned as 'suitable for clothing' above.
2. You can sew 'clothing thickness' leathers on an ordinary sewing machine. For 'furniture thickness' leathers, you would need an industrial sewing machine.
3. You could sew leather using something like a denim needle, but I strongly recommend you get leather needles. And ordinary needle has a point and sort of pokes holes into the material. A leather needle has a knife-like tip which allows it to cut into the leather. This means it puts less stress on the leather and on your sewing machine.
4. Leather doesn't behave like fabric under your presser foot and, as a natural product it can be uneven in texture. It can 'stick' or stretch in places. How bad this is differs per piece of leather and per sewing machine. So, always try out on a scrap first. Using a teflon- or roller foot often helps. If nothing else will help, sandwich the leather between strips of tracing paper, stitch through all layers and tear away the paper afterwards.
5. Make sure you don't have to unpick anything and if it can't be avoided, sew you new seam next to the old one, further into the pattern piece. The holes of the seam are there to stay.
6. Use a narrow seam allowance. 1 cm is enough for a material that can't fray. And you can't alter to make it bigger by letting out the seam a bit anyway, see point 5.
7. There is obviously no grainline in a piece of leather. So, take your pattern pieces and 'play Tetris' to put them as close together as possible, making the most of your material.
8. Leather can't be ironed, so to make the seam allowances lie flat, use glue. Any glue which is claimed to work on leather will do, but try out on a scrap first. You don't want to use a glue which makes your seams hard.
9. Think about the pattern you use. With leather, you could, for example, decide to have unfinished hems or to stitch some of the seams on the outside. However you should avoided crossing seams as much as possible. Seam allowances in leather stay very bulky in comparison to those in fabric.
I hope I've covered all of the subjects which raised questions. If there is anything else you want to know about sewing with leather, just leave a comment.