Material Evidence: Cahill (1987)

3). PIXE 1987

Cahill measures the titanium content of the VM.
Cahill, T, A, et al. 1987 The Vinland Map, revisited: new compositional evidence on its inks and parchment. Anal. Chem. 59, 829-833.

Pixe
The device accelerates protons that crash into the map causing x-rays to be emitted, each characteristic of the elements in the map. PIXE stands for proton-induced x-ray emission.

BACKGROUND:

PIXE - proton-induced X-ray emission - reveals which elements are present and how much of each is present. McCrone had identified modern titanium dioxide anatase in the ink, using microscopy. Here Cahill uses PIXE to check this, measuring the titanium content of some 200 samples from the VM, TR and SH.

McCrone's microscope measured the titanium content of individual particles on the ink line. The probe in the PIXE technique is very much larger, measuring the titanium content over areas greater than that occupied by the ink line. The titanium content of the ink is then a difference of two measurements - first for an area of parchment with ink, and then for an area without ink. The techniques are very different and it isn't clear how they should be compared.

FINDINGS:

PIXE Graph
What is present in the map? The energies of the x-rays identify the elements present and the peak heights record their relative amounts.
  • The ink on the TR and SH is iron gall ink. the ink on the VM cannot be identified.
  • The TR and SH contain no titanium.
  • Cahill finds only trace amounts of titanium on the VM, rejecting McCrone's findings and conclusions.

COMMENTARY:

  • McCrone had reported up to 30% titanium in the ink line. Cahill reports no more than 0.0062% titanium, less by a factor of 10,000.
  • Can these numbers be reconciled? McCrone examined individual particles in the ink, 10-3mm in length. PIXE measures titanium content over areas of 1mm2. McCrone only samples the ink layer, 10-3mm deep: PIXE samples ink layer + parchment, 10-1mm deep.

QUESTIONS:

  • Do McCrone's and Cahill's measurements of titanium content contradict each other?
  • McCrone identified the VM as a fake. Do Cahill's results invalidate McCrone's claim?