Curiously, despite recently counselling against the polishing of brasses in Furniture Brasses, a couple of readers emailed me asking how best to go about polishing them. Instanter I referred to Miss Leslie’s House Book for the unequivocal answer which I will also now share with the wider readership:
Dissolve in a pint of soft water an ounce of oxalic acid, (which is poisonous and should be well taken care of,) and keep it in a bottle labelled “Poison.” Always shake it well before using it. Rub it on the brass with a flannel, and then take a dry flannel to polish it. Use this solution twice a week, and next day have ready some pulverized rotten-stone, sifted through a muslin rag, and mixed with oil of turpentine, so as to be liquid. Rub this on with a buckskin, let it rest ten minutes, and then wipe it off with a cloth.
In cleaning brass handles, hold the handle firmly with one hand, while you clean with the other, otherwise the handles will soon become loosened by the unsteadiness of the friction. Lay underneath an old newspaper, to catch the droppings.
Oxalic acid being poisonous, care must be taken that none of the liquid gets into the eyes, when used for rubbing. Should this by any accident happen, immediately get a bowl full to the brim of cold water, and hold the eyes open in it, till the pain abates; repeating it at intervals during the day.
To remove the stain of oxalic acid from a dress, rub the spot with a sponge dipped in hartshorn [aqueous ammonia] diluted with a little water; this will cause it almost immediately to disappear. 
The message in all this is quite clear (except for the part about having to lay under an old newspaper while catching droppings); if you cannot resist the temptation to polish antique furniture brasses, then it is advisable not to wear your best dress for the occasion.
 Eliza Leslie, The House Book, or, A Manual of Domestic Economy, Carey & Hart, Philadelphia, 1838, p. 218.