USB Hand-held microscopes cost less than $200 but turn out very useful in all those cases where you cannot take samples to put under a compound microscope. A USB microscope is essentially a macro lens, the magnification is restricted and is not comparable to a standard compound light microscope but features such as grain size for mineral pigments and retouches crossing craquelure can be documented. I blog here on the images I took using a Veho VMS 2 Mega pixel.
Hand Held microscope Veho VMS 2 Mega pixel. I used this microscope for the images presented in this blog.
Calibration. I strongly suggest to buy a Stage Micrometer Calibration Slide. You find it on eBay for about $30. They are mandatory in order to calibrate your microscope so that you know exactly the size of what you are measuring. They have divisions up to 0.01 mm so that you can calibrate your microscope until 10 microns.
Stage Micrometer Calibration Slide with 0,01 mm (10 microns) divisions.
Veho VMS has two magnifications. Looking at the Calibration Slide with the lower magnification we can just observe the 1 mm line.
Calibration slide seen at lower magnification with Veho microscope. Only the 1 mm line inside a circle is distinguishable.
At the higher magnification we can distinguish the 0,01 mm (10 microns) divisions inside the 1 mm line. Not bad for a less than $100 microscope.
Calibration slide seen at higher magnification with Veho microscope. The 0.01 mm (10 microns) divisions are distinguishable.
Software. These microscopes come with a bundled software. Though, I prefer a free software, MICAM, download here.It works with any of these USB microscope and let you calibrate your microscope with a calibration slide.
Pigments. I tried Veho VMS hand-held microscope on my collection of gum Arabic painted swatches of historical pigments.
Yellow Pigments swatches observed with a USB microscope
I also have microscope mounted slides of the same pigments, so it is useful to compare how pigments look both painted and dry on a prepared slide of dry pigments and Cargile meltmount.
Pigments microscopy slides prepared with Cargile meltmount.
Below are some observations.
Cadmium red. Synthetic pigments have grains smaller than 1 micron and cannot be detected.
Red ochre (gum Arabic swatch). Natural mineral pigments such as red ochre are characterized by grains of different size and colors.
Red ochre (mounted slide) is heterogeneous in both size and color of grains.
Vermilion (gum Arabic swatch) shows many dispersed black grains. Indeed, vermilion is known for degradation and blackening.
Green earth (gum Arabic swatch) looks heterogeneous both in color and size of the grains.
Green earth (mounted slide). It’s characterized by heterogeneous distribution of minerals in size and colors.
A mineral pigment such as malachite (gum Arabic swatch) exhibits a richer texture than industrial pigments such as cobalt green (below).
Malachite (mounted slide). Its crystals are well defined and well compares with the image of the malachite on gum Arabic swatch.
Industrial pigments such as cobalt green (gum Arabic swatch) are perfectly homogeneous and do not show any texture.
Verdigris (gum Arabic swatch) is characterized by well defined crystals. This variety was pretty course.
Azurite (gum Arabic swatch) has defined crystals homogeneous in size and color.
Ultramarine natural (gum Arabic swatch) has characteristic white inclusions.
Ultramarine natural (mounted slide). It has characteristic white inclusions.
Observation on early 1900 paintings.
Hand-held microscope can be used to check the size, color and shape of pigments grains directly on the surface of a painting.
Retouches are clearly over original craquelure.
Observation on the painting. The blue pigment in the sky is a ground mineral since it exhibits large blue grains. Probably ultramarine as suggested by the infrared false color.
This video shows that you can take great video with an hand-held microscope which give a 3D feeling of the surface texture. details on this video are in this blog.
Canvases and textiles
An Hand-held microscope is a perfect tool for thread counting. Once calibrated to shot a 10×10 mm image it allows to characterize the canvas in terms of thread count (in this image 14/12 cm).
Inks and pencils.
This image — taken from a written canvas — shows the characteristic flakes of a pencil.
Ink writing. Compare this image with the one above to tell the difference between a pen writing with a fluid ink and a pencil.