Cleaning Brass by Electrolysis

[Nick]

Oxalic acid - you can get it in loads of places.

Including rhubarb leaves.

Indeed, which is why you shouldn't eat them... you can extract oxalic acid from rhubarb leaves, however, its far cheaper and easier to buy it !

Here a photo of some oak French doors that were BLACK with stain as they are completely exposed to the prevailing winds & weather (we are on top of a hill) - I used oxalic acid gel to clean them.... (Osmo sell it as their "wood reviver" but I made my own [eventually!] - the door on the left has been brushed with Osmo UV 420 oil - the one on the right is after oxalic treatment but before oiling)