Paper Chase - Hahnemuhle - The Art of Expression page 3

To OB or not to OB? – that is the question

Optical Brightening Agents (OBAs) are added to the base material, the surface coating or both, to make a paper look ‘brighter’. This occurs by a process known as fluorescence – light hitting an OBA is reflected back at a higher wavelength. Thus, short wavelength ultraviolet light is invisible to the eye, but is fluoresced out of the OBA as blue light. A paper containing OBAs can thus reflect back more than 100% of the visible light shining upon it (its natural reflectance, plus the fluorescent component). To the observer the paper appears both brighter and cooler. Conversely, OBA-free papers are warmer, creamier and less bright and usually more expensive if quality is to be preserved.

The downside of OBAs is that they cease working after long-term exposure to uv light and allow the creamier base of the paper to show though. The chemicals themselves may also yellow with age. This can be a quandary for the photographer, who may prefer the brightness of the OBA-containing print, but fear for the archival stability of the image. For many in the fine art community (and that includes, particularly, the fine art monochrome enthusiasts) OBAs are a complete ‘no-no’. You pay your money and make your choice, OBA-free papers have to be more refined in production and use more expensive rag products, often at 100%. In addition there can be issues when making icc profiles for papers containing OBAs. Unsophisticated spectrophotometers do not screen out the uv components of colour – they can ‘see’ them, even though the eye cannot. The result is a print that is over compensated towards yellow. This is one reason why scanner-based profiling solutions are not as accurate as spectro-based ones. It is also incidentally why OBA-free papers deliver better colour audit statistics – the gamut is matched to the base paper tone, dragging skin tones too blue in OBA-containing papers, whereas the OBA-free paper leaves them exactly at the right spot. The eye, of course, accommodates for this drift and so the error is not visually obvious even when the statistics detect the effect.

At Professional Imagemaker we always examine a paper in a special uv-booth as well as looking at the Spectral Power Distribution (SPD). The SPD is a fancy term for how the reflectance of a paper varies in different colours (wavelengths) of light. By looking at the SPD we can measure the lift of reflectance in the blue part of the spectrum over the base level for the rest of the spectrum. We also examine both the front and the back of the paper in the uv-booth. Any fluorescence on the back indicates that the OBA is contained in the body of the material. For high-value rag papers, the waste, trimmings and off-cuts are often recycled so that the coating seems to end up in the mix (good for the planet though!).

In the diagram, the high lift of Torchon is very evident. Photo Rag has a barely detectable lift, but the Museum Etching is hugely depressed at the 440nm wavelength. Photo Rag contains OBAs the body of the paper only.

Photo Rag 188, 308, 460 PhotoLine

Photo Rag is the material with which we are most familiar having made dozens (or even hundreds) of profiles over the years. It is the benchmark material that we use when reviewing printers. The material is available as 188, 308 and 460gsm weights and a number of other options that we will list and characterise separately. One profile will usually suffice for all the plain ‘Photo Rags’ including the double-sided Duo. When the coating differs (eg Silk, Pearl or Satin), a different profile would be in order, although differences might be marginal. The audit print obtained using the Hahnemühle profile had an average error of 7.4 LabΔE/4.0ΔE2000, reasonably typical for Epson K3 on a Photo Rag. We found that the use of VFA as the media setting was more neutral than WCRW as with the ArtLine series. Bespoke profiling of the Duo variant (see next media) reduced this error to 5.5LabΔE/3.26ΔE2000 which is again typical of the results we obtain.

In summary then Photo Rag remains the baseline from which other materials should be compared and our long-standing advice of choosing this material as your introduction to the range is as valid as ever. Although Photo Rag may be used with Photo Black ink (on the Epson 4800/7800 series) there is a penalty on Dmax and a slight loss of punch in the print – this is a problem that does not arise with the Epson 3800 as ink changing is a trivial matter.

Photo Rag Duo 276 PhotoLine

This is a new addition to the range in that it replaces the 316 and 196gsm materials in a rationalisation of the range. The surface of both sides are coated which makes the paper suitable for card-making and bespoke flyers should you wish to create a striking impression as you visit a gallery (eg image on one side with your contact details etc on the reverse). It could also be used in a portfolio with images on either side, saving both weight and money. There is a slight difference in the surface texture either side of the media so you may choose your preference for the ‘main’ side of your print.

Photo Rag Bright White 310 PhotoLine

This media is the baseline Photo Pag with additional OBA to make it even brighter, a request from the photographic community, we understand. Using the Hahnemühle profile and WCRW media setting produced an error of 5.0LabΔE/3.22ΔE2000, an excellent result. This was not improved statistically by the use of VFA media setting but the print was more neutral and the Dmax was lifted a couple of notches. The skin tone error was improved from 3.7 to 2.0 LabΔE but some people might actually prefer the slight tan applied by the WCRW setting. There was a slight hint of purple warmth to the VFA print when viewed in natural North Daylight reminiscent of a light selenium tone on a halide print. Metamerism was one of the lowest we have recorded at 0.9 LabΔE. Overall this is a combination that would benefit from the user experimenting and choosing the rendering of their liking, it is certainly worth investigating for the monochrome specialist who is not put off by OBAs.

Photo Rag Satin 310 PhotoLine

This is a smooth callendered finish to which an additional coating has been applied. This responds to the ink to create a light silky sheen to the print, which is very attractive. It is tailored towards retaining the maximum amount of detal in photographic reproduction but retains an art feel with its weight and texture. It is a surface we like a lot. The surface may be used with Matte Black ink and so it offers an alternative to Epson 4800/7800 users who habitually use Matte Black but do not wish to perform an ink change to create a satin print from the pearl finishes currently so popular (and represented in this review by Fine Art Pearl). Epson 3800, Canon and HP users do not have this dilemma with the speedy and inexpensive in change available.

Natural Art Duo 256 PhotoLine

This paper is effectively an upgrade from the 216 variant of the same name. It lifts it into compliance with Fine Art Trade Guild standards for giclée but increased was mainly done to overcome see-through with the thinner weight. IN the absence of a data sheet we have assumed that the coating is the same as the original and used the Hahnemühle profile from the web site with a VFA setting. The audit data are much in accord with similar matte, art papas free of OBAs. That is a depressed Dmax and accurate skin colours in the hue and saturation channels. The two sides a subtly different in texture and we printed to both. The ‘signature’ of the colour errors was almost identical and the couple of tenths of a point here and there was probably data noise – to all intents the colours were identical on each side and the only difference is the textural properties. (In the graph shown there are actually two sets of data superimposed, one over the other – you can only detect a double line in the deep red.) This makes this media a good candidate for double-sided portfolio preparation, although good practice would demand that you kept the paper surface orientations matched from sheet to sheet in a book.

Photo Rag Pearl 320 PhotoLine

This is a new, OBA-free, 100% cotton rag, natural white media equipped with the baryt-like surface coating. At a stroke, therefore, it fulfils all the demands of the fine art sticklers, but with the type of coating that is providing such good Dmax and colour precision data. The base colour is a natural cream.

Using the Hahnemühle profile from the website turned in a spectacular colour audit data complete with the skin tone accuracy we have found on other papers of this generic type. Bespoke profiling improved the audit data to 3.7LabΔE/2.33ΔE2000 another really top result. The skintone errors were as small as we have seen at 1.9LabΔE/1.5ΔE2000. The bespoke profile removed the slight yellow cast of the Hahnemühle profile to improve both the skin tones and in particular the grey error that was a very low 2.3ΔE2000. Metamerism was low at 1.4 LabΔE and the landscape colours turned in a good performance. In essence the values were very close to those obtained with Fine Art Pearl and so are not repeated here. You can obviously choose between these two products on aesthetics and OBA demands, secure in the knowledge that the colour performance is truly spectacular. The only problem we did note was that the paper was not driven accurately right through the printer with the very tail end showing some image ghosting (see image).

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Photo Quote: Some photographers take reality...and impose the domination of their own thought and spirit. Others come before reality more tenderly and a photograph to them is an instrument of love and revelation. - Ansel Adams