Magnifiers: a closer look (XVII)
NIR spectroscopy of loupe materials (part II)

In December we had discussed a magnifier with plastics lenses. The respective resin type of those lenses (acrylics) had been identified by means of Raman spectroscopy.

In addition we had illustrated in February that a very similar result might have been achieved by an other spectroscopic method, namely NIR spectroscopy.

The following recap is showing the SCiO^TM NIR spectra of some classical artificial resins (plastics). You won't need a diploma in physics or chemistry - simple image comparisons will help to perform the task:

Fig. 1: SCiO^TM NIR spectra of some classical plastics. CA: Cellulose acetate, CN: Cellulose nitrate, PC: Polycarbonatc, PMMA: Polymethyl methacrylate, PS: Polystyrene.

But we are not restricted to lens materials, of course. Magnifier mounting materials can be assessed as well. Just have a look at the following instrument, a combination of a letter opener with a magnifying lens. It was made ca. 100 years ago.

Fig. 2: A magnifier with ivory look - but without the killing of an elephant.

This is the NIR spectrum of its ivory imitation mounting material:

Fig. 3: The NIR spectrum (red line) of the mounting material of the magnifier shown in fig. 2, in comparison with a CN reference spectrum (green line):

The instrument shown in fig. 4 is of similar age (ca. 100 years again) with its mounting material intended to mimic tortoise shell:

Fig. 4: Magnifier, with "faux tortoise" mounting material.

Fig. 5: Close-up view of the instrument shown in fig. 4. The handle is made of a combination of silvery metal, plastics and fine copper pins - like stars on a dark sky!

Again NIR spectroscopy is well able to identify the plastics material, this time as cellulose acetate (in short: CA):

Fig. 6: SCiO NIR spectrum of the mounting material of the magnifier shown in fig. 4 and fig. 5. The spectrum of the magnifier material is represented by the red line, the comparison material cellulose acetate by the green line.

As a further indicator for the scope of this method we are going to show the spectrum of an automobile headlight "glass":

Fig. 7: The headlight material (red line) can be identified by comparison with a Polycarbonate (PC) reference spectrum..

Literature and further technical informations

A poster with a short characterisation of the SCiO spectrometer can be found here:
Tiny, "quick & dirty" NIR spectroscopy for the identification of plastics

Susanne Brunner and Martin Mach (2021): Tiny, 'quick and dirty'. NIR spectroscopy for the identification of plastics. In: Bechthold, T. (Ed.): Future Talks 2019. Surfaces. Lectures and workshops on the technology and conservation of the modern. Munich, p. 216-225.

The instrument used here is the basic version of the SCiO spectrometer which was available at a bargain price from the respective kickstarter project a few years ago.
Sadly, it appears that the low cost model is no more available (as the Consumer Physics company switched to a much more expensive licensing model based on yearly fees).

© Text, images and video clips by  Martin Mach  (webmaster@baertierchen.de).
The Water Bear web base is a licensed and revised version of the German language monthly magazine  Bärtierchen-Journal . Style and grammar amendments by native speakers are warmly welcomed.

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