LEDs part 2

How LEDs are now very much earning their keep. Conservation viewing aids and other useful pieces of equipment.

Definition of ‘light’: The natural agent that stimulates sight and makes things visible; the key words here being ‘makes things visible’.

Definition of to ‘illuminate’: to enlighten, as with knowledge, to make lucid or clear.

With such a large, diverse and dynamic collection here at the Fitzwilliam1it is hardly surprising that a lot of time is given over to preparing new displays, reviewing items destined for loan and supporting, at times complex in-house exhibitions.

Conservators are required to examine objects extremely closely and quite a lot of their time is spent carefully recording this information. Assessments are made with regard both damage and decay and then to diligently note perceivable change, especially over time. Furthermore, we must be able to establish the construction of an object, the materials that have been used, such as paper and drawing media, and in some instances even the order in which these have been applied.

Although light can be extremely damaging to a wide range of museum objects, its power with regard to illuminating collections can be fascinating and at times, revelatory. As such, both good light and good optics are essential.

Stand alone inspection lamps

To help in these tasks, the museum has recently acquired several stand – alone LED photographic lamps 2. These have replaced older fluorescent lamps which by comparison are somewhat harsh, one directional and at times prone to heating up.

Botticini, Francesco 1446-1497 (Florence). Virgin Adoring the Child, Tempera with gold on a wooden panel, M.10. Task lit using a versatile LED photographic lamp.

Useful features include: an ability to adjust both the levels of illumination and colour temperature and integrated rechargeable batteries, which offer the unit much greater flexibility of use.

A digital display on the back shows how this particular lamp is fully powered, it has a brightness setting of 71 % and a colour temperature of 4100 degrees Kelvin.

For conservators, the technology is now very much out there and the  options available are multiplying all the time. To some extent, the process of selection will be determined by personal preference and in many cases, the cost. Speaking from experience, investing in a good stand (one that is both stable and mobile) will pay dividends. The wheels on ours seem to have a mind of their own and tend to travel in only the one direction!

Hand held LED inspection lamps

The Docter Aspherilux Midi rechargeable LED Torch 3

German-made and the quality really shines through.

A compact torch which gives bright, directional light of even intensity. The metal casing is robust, the body is well balanced and the unit contains integrated rechargeable batteries. The only problem you may have with this particular torch is ‘holding onto it’. In our museum, at very least, useful things become popular with others!

Ambient studio lighting.
A strong and informative (directional) raking light.

This clearly shows the power of ‘raking light’ in revealing the paper undulations, embedded creases, ingrained dirt and other interesting surface textures. Invaluable!

Shown below is a portrait miniature of Charles, 1st Marquis Cornwallis (1738-1805), No 3922. Watercolour on ivory, by John Smart (British artist, 1741-1811) within a decorative gold locket, glazed. Dimensions: 67 x 52 mm.

Condition appears fine, or is it?
On closer inspection (lit by a strong raking light – underside of the cover glass) ‘all is not well’. Click on the image to enlarge.

The black arrow above shows a passage of glass clouding and although subtle, this is important, being indicative of the onset of glass disease4. If this condition is left indefinitely, especially in a poor environment, the sequence of deterioration would become very much more dramatic. As such, by having noticed the change and ideally acting accordingly, this is an important first step in any good preservation plan.

Ultra Violet LED lamp5

A compact Ultra Violet LED torch (Nite Ize, USA)

On occasion, examining an object under Ultra Violet light can be extremely rewarding as illustrated by the 16th century portrait miniature, shown below. In this case the yellowy – green fluorescence indicates  passages of loss, earlier damage and discrete later additions. This particular ‘visual marker’ is indicative of a 19th century pigment, Chinese White (zinc oxide)6.

Photographed in daylight.

Portrait miniature of Henry Frederick, Prince of Wales by Isaac Oliver (British artist, 1556(?)-1617) 3903. Watercolour on vellum laid to card. Dimensions: 52 x 40 mm.

Photographed under Ultra Violet where the edge damage and later additions are clearly visible. Click on the image to enlarge.

Magnifiers

An Optivisor is a useful and inexpensive viewing aid, costing approximately £30-50. This is the sort of thing that one often reaches for whilst inspecting an object at close quarters and is commonly used by paintings conservators engaged in detailed image reintegration -restorations.

Various lenses are available offering different powers of magnification and are easily interchanged. Personally, I have found x 4 most helpful for some of the more detailed conservation tasks.

In recent months here at the Fitzwilliam we have been taking a closer look at many of our miniature paintings7and for this task, I have found a small hand-held magnifier especially useful8.

Leuchtturm-Lighthouse frameless LED Illuminated Magnifier.
Seeing things in a better light.

Portrait miniature of an unknown man, PD.958-1963. Watercolour on ivory  by John Smart (British artist, 1741-1811) within a decorative gold locket, glazed. Dimensions: 38 x 32 mm.

Examining such small works as these under magnification and in good light, helps enormously in their interpretation. Close inspection is invaluable and may reveal all sorts of ‘collection care issues’; such as friable media and/or loss, the onset of glass disease or perhaps even, invasive mould growth (see the detailed image shown below).

An 18th century miniature portrait.

Portrait Miniature of Sir Joshua Reynolds by James Nixon, British artist, c.1741(?)-1812, No 3800. Watercolour on ivory, within a locket, glazed. Dimensions: 80 x 64 mm.

Scale in life: 40 x 60 mm (detail)

Detail of the same, showing invasive and unsightly mould to the surface. Click on the image to enlarge.

Under closer scrutiny, surface mould growth is clearly visible. Spotting this type of damage and taking the necessary action (ideally addressing the mould and being especially vigilant with regard ‘storage conditions’) is important, in any progressive collections care plan .

Conservators are naturally inquisitive creatures and often, through necessity, have had to evolve and adapt. The profession is relatively small and sadly, all too often poorly resourced. As such, borrowing ideas from others is especially satisfying and all the more so when this saves a little money.

LED Light panel – light box 

By way of example our studio recently purchased an LED ceiling light panel9,a chance find at a local electrical outlet. Although most frequently used in schools and hospitals, this even light source has now become our ‘go to’ studio light box.

A fortuitous find: how LED ceiling light panels are now doubling up as a useful, low profile, light box. A reliable, inexpensive source of transmitted light.

Transmitted light (light shone through a surface, such as a paper) is especially helpful in revealing certain characteristics that otherwise may remained hidden, such as a maker’s watermark or perhaps even, the date of manufacture.

A fan shown on an unilluminated LED light panel, nothing spectacular in itself.

 

The same in transmitted light. Note the physical damage (various losses and tears), information with regard the fan’s structure and the delicate fretwork pattern (small pieces of paper cut out by hand). Click on the image to enlarge.

 

In detail, unilluminated.

 

In detail, illuminated (showing the power of ‘transmitted light’)

M.219-2015: 18th century Italian chinoiserie fan. One of 600 or so, rich and varied fans recently acquired by the Fitzwilliam (2015)10.

As conservators we look for clues with regard the paper type, the process of manufacture, the probable age and perhaps even, a place of origin. This not only helps in our better understanding an object it may sometimes lead to more precise authentication.

Below is a watercolour by JMW Turner, photographed in day light.

Venice, storm at sunset by J M W Turner (British artist, British artist, 1775-1851) watercolour and bodycolour, Size 222 x 320 mm. Given by John Ruskin in 1861, No 590.
The same watercolour, photographed in transmitted light, using an LED light panel. Click on the image to enlarge.

When viewed in transmitted light the paper shown above is clearly wove11 and looking more closely, a maker’s watermark ‘J Whatman 1834’ can be seen, which is both of help and significance. Turner is known to have visited Venice on at least three occasions, in 1819, 1833 and 1840, although recent research has suggested that he was also there between 1835 and 1839. The light shining through the paper reveals an extensive inscription written on the back of the watercolour (possibly in Ruskin’s hand) and also gives useful insight into Turner’s working methods where he has scratched back the paper, creating highlights of both the Venice skyline and turbulence seen in in the sky and breaking waves.     

Dated watermarks do not prove the date of production but do provide a reference point of sorts, and it would be reasonable to assume that the work by Turner shown above could not have been produced any earlier. It could, however, have been produced several years later. Some artists are known to have preferred using a seasoned or aged paper, whereas others may have returned some years later to work up an incomplete sketch.

I hope that some of the illustrations presented above are of help and may stimulate others to look more closely and with that all-important ‘questioning eye’.

 

Acknowledgement: My thanks go to several kind colleagues for reading the text, helping with IT issues and for gently nudging me back on course.

 

 

LEDs Part 1 Seeing things in a new light

How LEDs are now very much earning their keep
Gallery lighting – setting the scene

The best type of gallery lighting should be versatile, easy to calibrate, natural in appearance and ideally, environmentally compliant.

In recent years the advances in Light Emitting Diodes (LEDs)1 have been little short of extraordinary. This is now an established lighting technology and is ‘absolutely where the future lies’, no ifs, no buts.

Here at the Fitzwilliam Museum most of the lighting, along with many other heritage institutions and art galleries, is predominantly by halogen incandescent2 and to a lesser extent, fluorescent lamps. Although well-honed and now quite sophisticated, there are downfalls: significant energy usage, local heat production and certain reliability issues. Furthermore, when compared to LEDs, incandescent lamps have a pitiful lifespan and to compound matters, the sourcing of suitable parts has become increasingly difficult.

Replacing bulbs can be time consuming, disruptive, and in certain situations it is not always easy to undertake without an element of risk.

The average life expectancy of a traditional incandescent bulb will be around 5 years whereas by way of comparison, an LED will be closer to 100. These statistics alone reveal a startling disparity, and one that increasingly just cannot be ignored.

Recent advances in LEDs have seen a broader range of lenses available and perhaps of more significance, a greater accuracy with regard their colour rendition. So, when the cumulative power saving projections alone are taken into consideration, the argument against their implementation falls pretty much at the first hurdle.

 

Selection of LEDs

When selecting the type of LED for gallery use, four important factors should be considered carefully The colour rendition index, colour temperature, wavelength profile and light output or illuminance.

Diligent research and seeking guidance from an established supplier will pay dividends. See also: ‘LED Decision-Making In a Nutshell’ by James R. Druzik and Stefan W. Michaliski, August 2012, pp. 22, 23.

 

Colour Rendition Index (CRI)

The effect of a light source on colour appearance is expressed by the CRI index, on a scale of 0-100.  Natural outdoor light has a CRI of 100 and is used by way of standard comparison.

CRI 60 – reasonable

CRI 70 – moderate

CRI 80 – good, reflecting colours ‘truly and naturally’

CRI 90 – excellent, a full and vibrant colour range (heritage organisations should be aiming for 90 plus). 

 

Colour temperature

The colour temperature of a lamp can be used to understand how the light will appear to the human eye. Measured in degrees Kelvin (K).

Both natural and emitted electrical light (various types) will be composed of different wavelengths. Light, from whatever the source, will have a unique profile and in turn a ‘specific colour temperature’.

 

Warm light           2,700 – 2,800 K

Neutral light         3,500 – 4,000 K

Cooler light           5,000 – 6,500 K      (simulates daylight)

Daylight at noon is generally cited as being around 5,600 K. However, in reality this figure will vary according to both the time of day and weather. 

 

Wavelengths

Measured in nanometres (nm)

 

Ultra-violet3 (UV) light waves fall below 400 nm and is invisible to the human eye. The lower the wavelength, the higher the frequency and potentially, more damaging to museum collections. UV should be excluded wherever possible.

By contrast, Infrared4 radiation is above around 750 nm at the higher end of the scale and will produce heat. Heat speeds up chemical reactions and this becomes relevant when caring for collections with regard the rates of decay and degradation.

The graphs below compare old incandescent lighting in the Flowers Gallery with newer LED lighting in the recently refurbished Dutch Gallery.

Correlated Colour Temperature: 2750 K

Colour Peak: 766.77 nm

Lighting: Incandescent lamps (Halogen) and some filtered daylight

 

 

Correlated Colour Temperature: 3761 K

Colour Peak: 545.82 nm

Lighting: LED (predominant gallery light source)

Skylights: Fluorescent tubes minimal filtered daylight

 

Wavelength profiles captured with a Spectrometer (GL Optic’s GL SPECTIS 1.0 touch) January 2017.

 

Light Output – Illuminance

Measured in Lux5

The illuminance considered appropriate for most gallery spaces will be dictated by both addressing audience need and the various sensitivities of the collections displayed (the material type, make-up and overall condition).

Taking a light reading6 in the Dutch Gallery. Oil on panel (detail) by Abraham van Calraet, 1642-1722.

Light levels and exposure should be carefully monitored and ideally logged, since light damage to museum objects is often subtle; the effects are cumulative and crucially, any change inflicted is irreversible.

By way of an example see the drawing below where the cut away top mount shows just how drastic the change can be.

Black and white chalk drawing on a coloured paper by Walter Sickert, 1860-1942 (detail).

In this particular case, the coloured paper support was originally and entirely, a greenish blue. The colour shift from green to brown, where the drawing has been exposed to light, alters both the look and quite possibly, the intended context. Fortunately, such extreme examples are rare within museums and as conservators, we always endeavour to keep it this way.

A computer generated overlay gives an impression of how this drawing would have originally looked.

 

Intelligent lighting design: Creating a sense of theatre

With carefully calibrated light levels, directional beams and consideration to the colour balance (within the range of whites) the impact of intelligent lighting can be little short of ‘transformative’. As such, many of the more informed galleries are now making good use of specialist lighting designers.

 

An example of exhibition lighting here at the Fitzwilliam Museum:
Degas: A Passion for perfection (2017).

Wall mounted art works and a cased table top display, carefully lit.

 

Bronze Spanish Dancer (foreground), posthumous cast, by Edgar Degas.

In the above two examples both the needs of the museum objects and the overall gallery lighting has been planned.

 

The recently refurbished Dutch Gallery (2014)

As part of a recent refurbishment project in one of the galleries here at the Fitzwilliam Museum, various lighting modifications were considered. The museum adapted – it embraced change and now this particular gallery is predominantly LED lit.

The Dutch Gallery with a c1690-1700 Flower Vase (foreground) hosting, in this case, some convincing silk flowers. 7

Displaying a mixture of museum items within the same gallery space can present certain challenges since each item type will have a different tolerance.

As such, the most sensitive object will tend to dictate the parameters. In this particular gallery the light levels falling on the displays range between 80 – 130 Lux (UV excluded) and are fully compliant with current standards.

The Dutch Gallery (above) is a wonderful example of just how beautiful a space can become with careful consideration and resourcefulness. LED’s are now very much part of the conversation and with regard to a transition, it is not a question of if but when. For my money – the sooner the better.

 

Seeing things in a new lighthow LEDs are now very much earning their keep. Part 2 will follow in the coming months. Various pieces of studio equipment making use of LEDs will be further investigated and discussed.

 

Further reading

The Museum Environment, (second edition), Gary Thomson, ISBN 978-0-7506-2041-3 Butterworth-Heinemann

Lighting for the built environment LG8: Lighting for museums and art galleries (The Society of Light and Lighting) ISBN 978-1-906846-7

Guidelines for Selecting Solid-State Lighting for Museums, James R. Druzik and Stefan W. Michalski, August 2012 (Canadian Conservation Institute & The Getty Conservation Institute) pp 22, 23 ‘LED Decision-Making In a Nutshell’

Lighting Industry Liaison Group, A guide to the specification of LED lighting products, 2012

 

Thanks go to my many kind colleagues, including the photographic team here at the Fitzwilliam Museum, Helena Rodwell in Collections Care and to Richard Carpenter, our PDP Technician, for quite literally giving me a hand (his right hand in ‘taking a light reading’). Lastly, to Gwendoline Lemée, for her invaluable guidance and ever cheerful encouragement.

 

 

It’s on my Christmas list: The Hirox 3 D Digital Microscope

Earlier in the year a small group of Fitzwilliam conservators were given  fascinating insight into the new and latest Hirox 3D Digital Microscope, PC Edition (RH-2000). A pretty sophisticated bit of ‘non destructive analytical kit’ by any comparison. Neat and tidy, with an impressive ability to process complex data fast.

As is often the case in conservation this technology has been developed for and embraced by other industries requiring ‘close scrutiny and exacting quality control’ such as precision engineering, electronics and other fast emerging fields such as nanotechnology. So, conservation sitting on these rather better funded coattails by way of mutual benefit, is no bad thing. Thank you, Formula One.

On the day, the brothers Alessandro and Marco Brecciaroli (representing Hirox) smoothly and in a charming way, guided us through the system. All too often in life it is difficult to make the full and appropriate use of a piece of equipment until one knows ‘just what it may be capable of’ and believe you me, Hirox is no slouch!

We were keen to see just how such a clever microscope could help in the field of Conservation. Could it extend the parameters of observation and perhaps more specifically, enhance our understanding. Quite possibly, and as such, this was an opportunity too good to miss.

Several of us brought museum objects with us on the day, mostly small and necessarily portable by way of putting Hirox through its paces – real objects under real scrutiny.

These included an early stained glass fragment, a painted swatch of powdery blue pigment, an intriguing small Egyptian coffin, a pre prepared pigment cross section cast in resin and a surface detail from a rare 19th century French watercolour painting.

Early stained glass fragment

      Post medieval stained glass panel (4230a Department of Applied Arts)
     A studio photograph using a conventional camera

Hirox got up close and personal and the revelations, to say the very least, were impressive.

 

In the detail above, courtesy of Hirox, we see the black tracing line,  subsequent coating of blue enamel and the surface disruption to the glass below. 

The glass surface is mildly scratched, it contains inclusions of sand (most probably silicate not fully melted during the original glass making process) and has a number of small ‘alluring air bubbles’, held captive since the middle of the seventeenth century!

The decorative element is now cracked and there are several small losses. As such, this particular artefact is somewhat at risk from further flaking.

Key features of Hirox

-Wonderful graphic quality, breath-taking magnification and the ability to capture and merge multiple images and/or create videos. And if that were not enough Hirox can be fitted with an endoscope enabling the investigation inside of an object.

-Uncompromising picture sharpness and reduced Digital Noise by way of ‘smart focusing’ and a camera that boasts the capacity to take somewhere between 50-100 frames per second, all at high resolution (1920 x 1200 pixel).

-Lighting is versatile, delivered by Light Emitting Diodes (LEDs) at a colour temperature of 5700 Kelvin. Various options include: Reflected, Transmitted, Bright Field / Dark Field and Polarization. Lighting with an Ultra Violet spectral range of 200-400 nanometres is also available if required. It would be prudent to check on both the emitted and cumulative light levels in particular and with regard any potentially light sensitive items.

-A broad range of high quality lenses are available anywhere from 1:1 to a staggering 10,000 x and numerous variant thereof. The changing of lenses appeared quick and easy by way of a bayonet fitting.

 

What soon became clear is that the examination of a small sample size and/or object was somewhat easier. For larger items one would require more careful planning and adequate space in order to engage the services of a bespoke and importantly ‘stable jig’.

Another option includes the use of a portable contact hand held lens.

Painted swatch of powdery blue pigment

Something as simple as the inclusion of a scale, seen here below in ‘microns’, is especially useful whether making a passing assessment or perhaps more so, by way of any future comparison.

The above image illustrates a powdery blue pigment part coated with a white waxy Cyclododecane1 consolidant –  in this case applied via an aerosol and now part sublimated  (evaporated).

Small Egyptian coffin

c. 600 BC / before the Common Era

The coffin surface is heavily deteriorated leaving very little of the original decoration and as such, one is left searching for clues. Hirox affords a different viewpoint and to some extent ‘a journey into the unknown’.

A small Egyptian wooden Coffin (E.43. 1907 Department of Antiquities)
44 cm (L), 13 cm (W), 14 cm (D)

Video footage across the coffin surface

The pigment trace seen in this short video is Egyptian Blue2. The remnant is trapped in one of the cracks of the coffin’s surface and although not wholly surprising it does indicate that the entire ‘wig decoration’ would have originally been painted in blue. This sort of information not only helps in our understanding of the object but it also allows for a far more accurate interpretation.

Pigment cross section

An example of a ‘stitched image’ captured by Hirox

Calcium ground      Egyptian Blue pigment           Varnish layer

Cross section of a paint sample containing Egyptian Blue (in this case a minute pigment sample was cast in resin and polished, prior to viewing).

19th century French watercolour

France, Normandy to be precise. The handy work of just who ?

This rare artwork will be on display at the Fitzwilliam Museum in the autumn of 2017 in what promises to be an exquisite show. The maker will be revealed and much more besides.

A gum glaze over watercolour         Surface abrasion

A close surface detail of a watercolour painting showing assorted fingerprints and other interesting information

3 dimensional modelling

Art meets science and maths, ooh and some pretty impressive graphics.

Real time measurements including length, angle and the surface area can be captured detailing the terrain and presented various styles. For obvious reasons, this sort of data could prove invaluable by way of comparison should the need arise, post loan or perhaps, assisting with an on going object ‘condition appraisal’.

3D Modelling of the powdery blue pigment part surface coated with Cyclododecane wax (see the earlier image of the same by way of comparison)

Like so many things in life, in order to capitalize on any investment (prices start from around £60,000 at the time of writing) one would have to give Hirox time and with that time one could reap bountiful rewards.

As such, I remain hopeful this Christmas!

 

For more information visit:

www.hirox.com

Alex Brecciaroli, Sales & Technical UK

alex@sharedlabseurope.com

www.sharedlabseurope.com

 

Thanks go to Alessandro and Marco Brecciaroli for their captivating  introduction to this impressive piece of equipment and also, to my many ‘kind and resourceful’ museum colleagues.