Arkwright Scholars Workshop

Saturday 26th November 2016

The two previous workshops for Arkwright Scholars on the uses of the optical microscope were a success, and so another was held this year in the same location, the Angela Marmont Centre in the Natural History Museum in London. The Arkwright Engineering Scholarships are awarded by the Arkwright Scholarships Trust and support students through their A Levels or Scottish Highers and provide financial assistance to help them pursue engineering, computing or technical design at university or through a higher-level apprenticeship. The Scholarships are sponsored by industrial companies, universities, charitable trusts, trade associations, professional engineering institutions, the Armed Services, Worshipful Companies, industry regulators or personal donors. Quekett members Dennis Fullwood, Pam H., Mary Morris, James Rider, Paul Smith and Alan Wood assisted at the workshop.

Pam Hamer introducing the workshopPam H. introducing the workshop

Theory of optics

We started with some theory of optics, including refractive index, refraction and diffraction, and how diffraction affects resolution (the detail that can be observed).

Measuring refractive index of a plastic blockMeasuring refractive index of a plastic block

We then showed the Scholars how to arrange 2 simple positive lenses to function as a basic compound microscope, with the first lens (objective) providing all of the resolution and some magnification, and the second lens (eyepiece) providing additional magnification.

Making a microscopeMaking a microscope

Stereo and compound microscopes

After the theory, the Scholars were talked through setting up their stereo and compound microscopes, to get the best possible illumination and to adjust them for individual eyesight. The Museum kindly provided 6 Leitz EZ4 zoom stereomicroscopes (8× to 35×) and 6 Olympus CX41 compound microscopes with 10×, 20×, 40× and 100× phase contrast objectives and substage condensers that could provide bright field, dark ground and phase contrast.

With 6 Quekett members and 12 Scholars we were able to provide a good level of assistance when needed.

Dennis FullwoodDennis Fullwood

marry-morris-scholars-2016-arkwright-720Mary Morris

James RiderJames Rider

Pam HamerPam H.

Carbon tooling laminate

With their microscopes properly set up, the Scholars were introduced to the 2 composite materials that had been provided by Solvay, one of the Arkwright sponsors. One was a carbon tooling laminate containing carbon-fibre and glass-fibre mats; sections had been made from this, and samples of fibres were provided. The laminate was of a type used on high-performance boats and cars.

Laminate materialCarbon tooling laminate material

The Scholars were provided with prepared microscope slides of carbon fibres and glass fibres (with human hair and spider silk for comparison), and were shown how to examine these using the Olympus compound microscopes. They used not only standard bright-field illumination but also 2 methods that provide enhanced contrast, dark ground and phase contrast.

Carbon fibres and glass fibres under the compound microscopeCarbon fibres and glass fibres under the compound microscope [by Pam H.]

Carbon fibres and a brown human hairCarbon fibres (7 µm diameter) and a brown human hair (compound microscope, bright-field illumination)

The Scholars were surprised to see the huge difference that lighting techniques can make to the appearance of a specimen under a microscope.

Carbon fibres, glass fibres and spider silk (compound microscope, bright-field illumination)Carbon fibres, glass fibres and spider silk (compound microscope, bright-field illumination)

Carbon fibres, glass fibres and spider silk (compound microscope, dark-ground illumination)Carbon fibres, glass fibres and spider silk (compound microscope, dark-ground illumination)

Carbon fibres, glass fibres and spider silk (compound microscope, phase-contrast illumination)Carbon fibres, glass fibres and spider silk (compound microscope, phase-contrast illumination)

Sections of the laminate (approximately 22×6 mm) that had been mounted in resin and then polished were provided for examination under the Leitz stereomicroscopes, and the Scholars were set the task of calculating the percentage occupied by voids in the exposed surface.

Laminate section mounted in a resin cylinderLaminate section mounted in a resin cylinder

Laminate with voidsLaminate with voids (macro lens, oblique reflected light)

Voids in laminateLaminate with voids (metallurgical microscope, vertical reflected light)

Glass fibre and carbon fibre mats of the type embedded in the laminateGlass fibre (left) and carbon fibre mats of the type embedded in the laminate [by Pam H.]

An inverted metallurgical microscope that uses reflected light for observing opaque subjects was also provided for examining the sections of laminates. This has a fixed, flat stage at the top, allowing large and heavy specimens to be examined, and uses prisms or semi-silvered mirrors to direct light through the objective onto a reflective subject. The objectives on this microscope are corrected for observing uncovered subjects, unlike those on the Olympus microscopes that are corrected for specimens under a 0.17 mm glass coverslip.

Inverted metallurgical microscopeInverted Gillett & Sibert Monolynx reflected-light microscope, with laminate section viewed from underneath

Sections through carbon fibres (7µm diameter) in laminate (metallurgical microscope, vertical reflected light)Sections through carbon fibres (7µm diameter) in laminate (metallurgical microscope, vertical reflected light)

Climbing drum peel test coupon

The other subject provided by Solvay was a climbing drum peel test coupon (a honeycomb sandwiched between 2 metal sheets, used for crumple zones on cars). One metal sheet had been peeled back to determine the bond strength, and this then made it possible to observe bubbles (faults) in the blue adhesive and the size and shape of the adhesive fillets produced during bonding. Specimens of this size are best observed with a stereomicroscope.

Climbing drum peel test couponClimbing drum peel test coupon, showing gaps in the adhesive layer

Other specimens and techniques

After the engineering examples had been thoroughly examined, there was time to introduce the Scholars to other microscopical techniques and specimens.

Pam H. showed some slides of effect pigments in eye shadow and blue paint, counterfeit £1 coins, security features in the new polymer £5 notes, and microfossils.

Eye shadowEye shadow containing effect pigments

Blue paintBlue paint containing effect pigments

The design of £1 coins has not changed in 30 years and about 3% of those in circulation are counterfeit. If you check your change you may be able to spot counterfeits. A new £1 design with state of the art security features will be introduced in March 2017.

Counterfeit £1 coinsCounterfeit and genuine £1 coins

The polymer £5 notes that were introduced in September 2016 have several security features:

Security features in polymer £5 notesSecurity features in polymer £5 notes

Microfossils in limestone rocksMicrofossils in limestone rocks

Microfossils mounted on a slideMicrofossils mounted on a slide

Dennis Fullwood got the Scholars to test their powers of observation by giving them one spent .223 cartridge case and asking them to find another one that had the same pattern left by the firing pin and therefore had been fired from the same rifle. The Leitz stereomicroscopes were used for this.

Pattern left by firing pin on a spent .223 cartridge casePattern left by firing pin on a spent .223 cartridge case, best viewed under a stereomicroscope

Dennis also provided some feathers from the corona of peacocks, demonstrated how to prepare a dry mount (the specimen is in air, not in a liquid or solid mountant) and then guided the participants through preparing their own slides that they could take home.

Feather from corona of a peacock, best viewed under a stereomicroscopeFeather from corona of a peacock, best viewed under a stereomicroscope

Dennis also showed several prepared microscope slides, Baltic amber containing insects, and some locusts.

Prepared microscope slidesPrepared microscope slides

Insects in 40-million year old Baltic amberInsects in 40-million year old Baltic amber

LocustLocust

Photos of the Scholars

Here are some more photographs of the Scholars during the workshop; they used their mobile phones to take photographs of the specimens, by carefully positioning them over one of the microscope eyepieces.

Scholars with microscopes

Female scholar with mobile phone

Two female scholars with mobile phone

Two male scholars

 

Two books by Quekett members were given to each Scholar: Understanding and Using the Stereomicroscope by Lewis Woolnough and Understanding and Using the Light Microscope by Dr Chris Thomas and Lewis Woolnough.

Report and photographs by Alan Wood

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