The role of terahertz polariton absorption in the characterization of crystalline iron sulfate hydrates.

Iron sulfate compounds have been used extensively to produce iron gall ink, a widely used writing ink in the western world from the 12th-20th centuries. Iron gall ink is well known to corrode writing supports, so detection of iron species is important for the preservation of historical artwork and documents. Iron(ii) sulfate readily changes hydration states and oxidizes in ambient conditions, forming compounds that contribute to this deterioration.

Assignment of the terahertz spectra of crystalline copper sulfate and its hydrates via solid-state density functional theory.

Terahertz (THz) vibrational spectroscopy is a promising tool for the nondestructive and potentially noninvasive characterization of historical objects, which can provide information on the materials used for their production as well as identify and monitor their chemical degradation. Copper sulfate (CuSO4) has drawn interest due to its inclusion in the preparation of iron gall inks found in historical artwork and documents. Copper sulfate rapidly forms hydrates which contribute to the formulation of these ink species and may influence their corrosive nature.

Systematic study of terahertz time-domain spectra of historically informed black inks.

The potential of terahertz-time domain spectroscopy (THz-TDS) as a diagnostic tool for studies of inks in historical documents is investigated in this paper. Transmission mode THz-TDS was performed on historically informed model writing and drawing inks. Carbon black, bistre and sepia inks show featureless spectra between 5 and 75 cm(-1) (0.