Our best and quickest acting remover was hydrofluoric. It seems to be more difficult to source now and the other chemicals suppliers sell are just not as effective, quite often leaving faint residues. This extract may be helpful - from a conservation site for museum boffins
roro
"Textiles with iron rust stains can be treated with any of the following chemical solutions:
- 5 percent hydrochloric acid [muriatic acid (HCl)]
- 5 percent oxalic acid H2C2O4
- 10 percent hydrofluoric acid (HF)
- 5 percent EDTA disodium
- 5 percent acetic acid (CH3COOH)
- 5 percent formic acid (HCOOH or CH2O2)
- 2-10 percent ammonium citrate
Oxalic acid and hydrofluoric acid solutions are the most effective for removing iron stains from archaeological textiles. Extreme caution must be taken, however, when handling hydrofluoric acid. EDTA disodium and ammonium citrate solutions are often recommended because their higher pHs (>2.5) potentially do less damage to fibers. These solutions are effective but rather slow. After any chemical treatment, intensive rinsing in de-ionized water will remove all residue from the textile which may adversely affect the fibers over time."