Ageing of laboratory irongall inks studied by reflectance spectrometry

This study tackles changes in colour of irongall inks over time. Different chemical processes, in which ink composition has a major influence, cause c olour change. Two series of inks were prepared, one using ferrous sulfate p artially oxidized, and another using pure ferrous sulfate hepta-hydrated; p ure garlic acid and gum arabic. The inks were applied on Whatman filter pap er, and then aged in a climatic chamber. The colour of ink spots was measured with a spectrophotometer. Changes in l ightness, chroma and hue were related with ink composition. All inks become darker and browner after ageing, including those not containing gallic aci d. Inks prepared with an iron/gallic ratio nearer to that needed for the co mplex formation are the darkest ones initially and show the slightest chang e in colour. Gum arabic containing inks darken more than inks without it. S trong corrosion was observed in the aged dark spots.