those chem students should study up on acetic acid, which is all vinegar is - any concentration of 5% acetic acid will be about pH 2.5-3 .... normal commercial pickling vinegar is 7%, available at most stores around here, and what I've been using in electroplating experiments
horticultural vinegar [actually up to 20%] is probably not common at most garden stores, but is a specialty "organic grower approved" weed killer
look at cider vinegar that sells for $4 a gallon, and at Wallys place, there are numerous 'generic' cider vinegars that are white vinegar with "approved" additives
water and washing soda are as cheap or cheaper than vinegar and with the addition of minimal electric current do the job better, electrolysis takes off the rust without affecting the underlying metal [as does phosphoric acid], and a similar acting organic acid would be tannic acid, widely used in artifact conservation
Bill
