An interesting technique I’ve been reading about recently is chemical etching. As a young lad I often etched my own PCBs using letraset style transfers and ferric chloride. At Stroud college we used a adapted version of Autocad to design a PCB which was then printed out onto clear sheet. To transfer it to the pcb we used photo resistive spray paint and a UV lamp. I definitely recommend good ventilation for that.
Chemical etching can also be used for making mechanical parts. This works in the same way as PCB etching works but typically there is no substrate, just the material. Etching can be done on a range of metals and also on glass. Different chemicals are used for the different materials and pretty much all of them are hazardous so ensure you’ve got gloves and suitable containers to avoid spillage. Also plan in advance as to how you are going to dispose of the chemicals.
You can etch all the way through the material or etch a pattern on to the surface by leaving the part in the chemicals for a shorter time. Part etching or half etching is a good technique for creating labelling or graticule that might be otherwise difficult to create using tooling. It’s also highly effective on glass for creating a message or decorative pattern.