Inside is just some guitar electronics a 1 MOhm B Type poti and a 220 k ohm resistor, to get a nice volume curve.
The high resistor keeps the sound tight.
This volume box is switched into the effect loop of the amp (it works just for amps with effect loop).
It is very cheap and simple thing and more interesting is the design.
Step 1: Grinding
I scratched the alu enclosure very roughly. It should look very used.
Then I threw it into NaOH to remove the oxide layer on the aluminium. After this procedure I washed with destilled water.
Step 2: Aluminium Which Looks Like Iron
I wanted to make it look like a rust piece of metal. So I got myself red colour which is sold to paint trousers in the washing machine.
Now I took boiler attached a cable to it and one cable to the enclosure. The boiler was filled with the red powder, salt, acetic acid and water. But this won't bring the colour on the box.
So here comes some electrochemistry. I put an isolating material into the boiler under the enclosure and then I applied a low voltage adapter to this set up (9-12 V). Make sure the enclosure serves as cathode.
I left this set up running for 2 h.
Afterwards I washed it with clear water, and left it inside the water for 30 min. It looked like I imagined in the end.