Lighting for photographing artwork

[Benkip]

Hello all

I'm a painter (canvases not walls) and want to start photographing my paintings instead of paying someone to do it (because it can't be that difficult and the savings I make doing it myself will quickly cover the cost of the equipment).

I will be using the cross polarisation method to get rid of glare (i.e. a polarising gel over the light and then another over the lens).

What lighting kit would people recommend?

Is a flash preferable to a continuous light source for my purposes? And if so, why?

I have been recommended the Elinchrom BRX 500. Is there any reason not to choose these? Obviously I need a full continuous colour spectrum (I can't seem to find whether or not these fit the bill in this regard). My paintings are generally not huge but occasionally I go up to nearly 2 metres tall - will these be powerful enough for that size?

And what are the best neutral polarising gels/foils for the lights? Do all gels fit all lights and if not, what's the optimum combination?

Apologies for naive questions. I'm something of a newbie.

Many thanks in advance

Benjamin.

 

[Phil V]

Flash outputs the closest thing to daylight you will find. That’s why we recommend flash not continuous (continuous lights add temperature and CRI detail because they are compromised in these areas).

More important are the modifiers, buy 2 the same, id recommend large rectangular softboxes (over a metre) add a 3rd flash with a grid for surface detail if that’s something you might want to do.

The usual lighting setup is a light at either side approx 45deg but some experimentation might be needed, depending on surfaces etc.

 

[Phil V]

If you ring Lencarta with your requirements they’ll put together a kit that perfectly matches your needs.

 

[Terrywoodenpic]

In past times it was usual to use four flood lights (2 each side) set at 45 degrees, as this gives a fairl hard directioal light, that gives an even illuminations that will show the necessary texture, Some texture is needed to show brush strokes and structure.
Polarises are only some times need. It is better when they are not required. We always used a black painted cubicle for our copy work which we left as a permanent set up.

 

[Garry Edwards]

Yes, it's a simple enough process - just like painting
All flash units produce a full colour spectrum (CRI100). The only continuous light units that have a full colour spectrum are the sun, and some very old fashioned heat producing lights that would melt your planned cross polariser gels, therefore flash is the only option for you.
The Elinchrom BRX 500 is a perfectly capable flash, but you won't need that much power and you don't need to spend that much money - As Phil V suggests, speak to Lencarta.
You will need a pair of flash heads with a pair of good quality softboxes, of the same size and shape (to keep the process simple). Lencarta's Profold range is a very good choice, because they produce very even lighting, which you need. This model https://www.lencarta.com/all-products/softboxes/profold-folding-softbox-lencarta-70x100cm-sof030 will be fine for paintings measuring up to around 100cm on their short edge.
Cross-polarisation can be a bit of a pain and I would suggest that you see whether you need it or not. Start off by polarising just the camera lens, but get a LINEAR (design) polariser for the camera, not a circular (design) one. The linear design is slightly more effective and is the only one that will work with cross polarisation, should you find that you need it. You will need to focus your camera manually, but that won't be a problem.

If you do end up with linear gels to cross polarise the lights, there are only one or 2 makes available now and there are no bad ones. You simply fit them to the front of each softbox, using a high-tech fixing solution called sticky tape. They need to be oversize because of the need to rotate them to get the optional setting.

 

[Benkip]

Thanks chaps. Very good.

 

[sk66]

The linear design is slightly more effective and is the only one that will work with cross polarisation, should you find that you need it.

A CPL is a linear filter; it's an acronym for Circular Polarizer Linear filter. A CPL is a linear filter first, and then a quarter wave plate re-polarizes the light for the camera to use by imparting a rotation to it.
Using one for the lens works exactly the same as using a linear filter, plus it doesn't adversely affect AF/metering/viewfinder like a simple linear filter can... not that AF/metering functions are absolutely critical for product photography.

The reason for re-polarization, and the introduction of CPL's, is that the pellicle mirror in a modern camera (that directs some of the light to AF, and some of the light to the metering module/viewfinder) is also a linear filter/beam splitter... and if the light was left linear some/all of it might not get to where it is needed. I.e. not enough passes through the pellicle mirror (portion) and AF fails.

 

[Garry Edwards]

A CPL is a linear filter; it's an acronym for Circular Polarizer Linear filter. A CPL is a linear filter first, and then a quarter wave plate re-polarizes the light for the camera to use by imparting a rotation to it.
Using one for the lens works exactly the same as using a linear filter, plus it doesn't adversely affect AF/metering/viewfinder like a simple linear filter can... not that AF/metering functions are absolutely critical for product photography.

The reason for re-polarization is that the pellicle mirror in a modern camera (that directs some of the light to AF, and some of the light to the metering module/viewfinder) is also a linear filter/beam splitter... and if the light was left linear some/all of it might not get to where it is needed. I.e. none passes through the pellicle mirror (portion) and AF fails.

Fair enough, I didn't know that. I do remember though, must have been back in the 90's, when I was using cross-polarisation a lot, that CPL lens filters didn't work nearly as well as linear ones in conjuction with the linear lighting gels, and wonder whether the technology may have changed?
Mind you, there was another difference at that time because I was using them to display, photographically, the stresses in curved plastic materials for a specialist manufacturer, rather than to suppress reflections.

 

[sk66]

I would guess that there is some variability in how strict the linear polarization is at either end (i.e how tight the grid is and how much light loss/rejection it imparts).

Edit: I just had a quick look and it seems that linear filters can commonly have a transmission rate as low as 20% and as high as 50%, or something called the "extinction performance" which can range from 100:1 for economical sheet filters to 1M:1 for birefringent crystal filters... it gets a bit more complex than I care to know but, basically, not all linear filters are the same.

 

[Deleted member 49428]

So placing Two linear polarizers stacked and orientere at 90 degrees you turn ord the passing light 100% approx. What happens then if you introduce a third turned 45 degrees?

 

[sk66]

So placing Two linear polarizers stacked and orientere at 90 degrees you turn ord the passing light 100% approx. What happens then if you introduce a third turned 45 degrees?

I'm not quite sure I understand your wording, or if it's actually a serious question... but I'm not doing anything else right now. So....

You don't normally block 100% of the light in any situation... that would be pretty pointless for photography.

A linear filter is basically just a grid of lines (some are physically, others are functionally). With two stacked vertically in alignment (or only one), they only block one orientation but not completely... when stacked perpendicular (cross polarized) they block both/all orientations, but leave holes behind; i.e. some of all orientations still pass through. It's more like the filtration cuts off the peaks of the wavelength/orientation rather than blocking it entirely... it still lets some unfiltered light through at a lower intensity/strength.

If the grids are tighter then the linear filtration is more exact and less light is transmitted, and then when cross polarized the holes remaining are even smaller... this is basically how variable ND's function.
Adding another filter would then have an effect on whatever is transmitted through the holes ("third pass" filtration with less effect).

In this animation you can consider the second set of lines as either a second linear filter (cross polarization), or as a single linear filter rotating with the first set of lines being the vertical axis of polarized light.



There's actually 2 transmission measurements for a linear filter; T1 which is for light that is oriented parallel the filtration, and T2 for light that is perpendicular to the filtration... those are combined mathematically to determine the extinction performance ratio.
More information and math than I care to learn/retain here.

Of course unpolarized light doesn't have just two orientations, it is more/less random. But the even more complicated part is that the act of absorbing light imparts a certain amount of polarization to what is reflected... that's why a single pass of linear filtration (i.e. a CPL) can/will have some effect on any surface that absorbs some light (colored surfaces/water/glass/etc) but no effect on surfaces that reflect all of the light (chrome/mirror/etc).

 

[Birdy06]

I always try to take photographs of my paintings outside when it’s bright but overcast so you get even, diffused light. Obviously, this isn’t always possible but doable if you have a batch of work to photograph. Beyond that, if I need to, I just use daylight bulbs in my studio and adjust the WB as necessary. Is there any need to over complicate it?

 

[Snapper67]

I always try to take photographs of my paintings outside when it’s bright but overcast so you get even, diffused light. Obviously, this isn’t always possible but doable if you have a batch of work to photograph. Beyond that, if I need to, I just use daylight bulbs in my studio and adjust the WB as necessary. Is there any need to over complicate it?

Your requirements certainly sound a bit different than the OP's.

From the other thread :-

The images will be for many purposes including giclee printing at full size. And in any case I want the highest quality archive of my work that I can achieve (because once a painting sells, I generally never see it again).

https://www.talkphotography.co.uk/threads/best-dslr-mirrorless-for-photographing-artwork.688381/


Dougie.

 

[sk66]

So placing Two linear polarizers stacked and orientere at 90 degrees you turn ord the passing light 100% approx. What happens then if you introduce a third turned 45 degrees?

Aww hell, I just realized what you were getting at... introducing an intermediary filter at 45*

and I spent all that time making that amazing gif...

 

[sk66]

I always try to take photographs of my paintings outside when it’s bright but overcast so you get even, diffused light. Obviously, this isn’t always possible but doable if you have a batch of work to photograph. Beyond that, if I need to, I just use daylight bulbs in my studio and adjust the WB as necessary. Is there any need to over complicate it?

If I were doing this I would probably start with standard "copy lighting" (based on the specific goals). Then if I was having an issue add a single stage of filtration (CPL on the lens as most photographers probably have one already). If that's not working, or can't work (i.e. chrome frame), add a second stage of filtration to the light source (cross filter as needed). And if that's still not enough, add a third stage to the light source (same orientation to make it more restrictive).

 

[Birdy06]

Your requirements certainly sound a bit different than the OP's.

From the other thread :-

The images will be for many purposes including giclee printing at full size. And in any case I want the highest quality archive of my work that I can achieve (because once a painting sells, I generally never see it again).

https://www.talkphotography.co.uk/threads/best-dslr-mirrorless-for-photographing-artwork.688381/


Dougie.

Not really. I supply images to King and Mcgaw, which is a very well known publisher of fine art prints and have never had an issue. Obviously, the higher the quality the better, but seriously, don’t over complicate things (and spend a fortune in doing so).

 

[HoppyUK]

Not really. I supply images to King and Mcgaw, which is a very well known publisher of fine art prints and have never had an issue. Obviously, the higher the quality the better, but seriously, don’t over complicate things (and spend a fortune in doing so).

I'm all for not over complicating things, but that depends on the actual artwork and the nature of the paint surface. Matt surfaces like watercolours are pretty easy, but shiny oils and acrylics are very different, and large artworks are more difficult too.

 

[Birdy06]

I'm all for not over complicating things, but that depends on the actual artwork and the nature of the paint surface. Matt surfaces like watercolours are pretty easy, but shiny oils and acrylics are very different, and large artworks are more difficult too.

Acrylics mainly and upto about 7 feet at the largest dimension, although mostly a lot smaller and on canvas. All I’m saying is that there is probably a much better and more professional way to shoot paintings but you can certainly achieve perfectly acceptable files without the large expense (and storage issues) of pro lighting solutions. Natural daylight is difficult to beat for art imo.

 

[droj]

Daylight in a way is best for everything. It's what we're born to as humans on planet Earth - it embodies the natural. We have a deep connection with it.

But with a production schedule, artificial light can be handy. (1) It can be summoned to order. (2) Unlike daylight, it's predictable (can be managed).

It's about having a system that fits the circumstances.

 

[sk66]

Natural daylight is difficult to beat for art imo.

I suppose, if you have the luxury of waiting for a bright/overcast/dry day... you do live in the UK don't you?

 

[Garry Edwards]

Acrylics mainly and upto about 7 feet at the largest dimension, although mostly a lot smaller and on canvas. All I’m saying is that there is probably a much better and more professional way to shoot paintings but you can certainly achieve perfectly acceptable files without the large expense (and storage issues) of pro lighting solutions. Natural daylight is difficult to beat for art imo.

Natural daylight is fine. All that we need it to be is flat, with no hint of sun. And we need there to be no wind either, and of course we need to be able to get the camera dead square to the subject.
Put lighting, weather and access conditions together and the reasons to shoot a simple subject to a consistently acceptable standard in the controlled conditions of a studio become pretty convincing.

I think that this thread has got a bit over complicated. All that the OP needs is a pair of mid range studio flashes, a pair of decent quality softboxes of the right size, a pair of decent light stands and a radio trigger. A polariser for the camera lens will probably be helpful too, cross polarisation will almost certainly be an unecessary complication.

 

[Garry Edwards]

Daylight in a way is best for everything. It's what we're born to as humans on planet Earth - it embodies the natural. We have a deep connection with it.

But with a production schedule, artificial light can be handy. (1) It can be summoned to order. (2) Unlike daylight, it's predictable (can be managed).

It's about having a system that fits the circumstances.

A fair point but I'm the opposite. I'll admit to be a studio photographer but almost every outdoor pic I shoot has at least a touch of flash too. The only normal exception to this is when the subject is too far away to benefit.

 

[Deleted member 49428]

Aww hell, I just realized what you were getting at... introducing an intermediary filter at 45*

and I spent all that time making that amazing gif...

Sorry bout that. It looks great, your gif. Yes sliding in a third filter between the two turned 45 degrees. What happens to the light?
Ansver: while the light will be (almost) blocked with only the two at 90 degrees 25% of the light passing through the first filter will pass through the third with the 45 degrees angled one slided in.
We are offcource talking linear polarizers.

 

[HoppyUK]

Daylight in a way is best for everything. It's what we're born to as humans on planet Earth - it embodies the natural. We have a deep connection with it.

But with a production schedule, artificial light can be handy. (1) It can be summoned to order. (2) Unlike daylight, it's predictable (can be managed).

It's about having a system that fits the circumstances.

No, daylight is most definitely not always best, whatever the subject. In fact, it rarely is and such a claim doesn't stand up to a moment's scrutiny - which is why good photographers have always modified and enhanced it in some way with filters, darkroom techniques and reflectors through to photoshop and full lighting rigs.

Daylight has the benefit of convenience which is a seductive trap that many are happy to fall in to because changing it is often difficult, but acquiring the necessary skills and making the effort to apply them is what sorts the wheat from the chaff.

 

[droj]

daylight is most definitely not always best

How we might modify it is partly a question of the photographer's intent, though. What's best for one intent might not suit another. Different techniques lead to different outcomes.

Technical competence may be thought of as a basic, but isn't the same thing as artistic expression.

In the end, it's the nature of what an image communicates that matters.

 

[Garry Edwards]

How we might modify it is partly a question of the photographer's intent, though. What's best for one intent might not suit another. Different techniques lead to different outcomes.

Technical competence may be thought of as a basic, but isn't the same thing as artistic expression.

In the end, it's the nature of what an image communicates that matters.

And now we seem to be moving sideways (or backwards) to that indeterminable discussion about the relative merits of technique -v- creativity.
I've heard it all before - we all have - and I've learned, from countless time wasted in discussions with artisitic photographers, many of whom thought that I should offer them a job, that the terms artistic, creative, self-taught, instinctive, natural light, free thinking (and similar adjectives) generally translate into alternatives such as unlearned, unskilled, unthinking, unpracticed, lazy and so on.

Whist we can probably all agree that our images need to communicate emotion, that concept can only work alongside a reasonable level of technical competence because, without it, we can only produce results by luck, and we can only replicate them by means of even more luck.

I can just imagine our OP here, who puts all of his artisitic skills into producing valuable artwork that he then photographs with his phone, using daylight. As a mark of his success, all of his work gets sold of course, and all that he can show prospective future clients is his phone images. "Ahh, then there's this one, the brush strokes weren't really as shiny as this but it was a sunny day. My client loved this one, the colours have gone wrong somehow, something to do with the time of day I photographed it I think. This one was great too, the weather forecast said that it would rain as soon as the fog cleared so it looks a bit blurred but isn't really. This one isn't really twisted, just something to do with the angle. I'm sure you understand, I'm an artist, very creative and not into all of the technical stuff. If only I could show you the originals, you'd understand."

 

[HoppyUK]

How we might modify it is partly a question of the photographer's intent, though. What's best for one intent might not suit another. Different techniques lead to different outcomes.

Obviously enough. But what's your point?

Technical competence may be thought of as a basic, but isn't the same thing as artistic expression.

Without technical competence, any claims to art are dramatically reduced.

In the end, it's the nature of what an image communicates that matters.

That's an obvious low-brow statement masquerading as insight. Every photograph communicates something, even if it's just that the photographer is rubbish. How does it relate to 'daylight is best for everything'?

 

[droj]

That's an obvious low-brow statement masquerading as insight.

You're in a feisty mood today. Obvious? Low-brow?

we can probably all agree that our images need to communicate emotion

Emotion? Did someone mention emotion?

Without technical competence, any claims to art are dramatically reduced.

Most of the time, yes, this is basic, except that within the overall gamut of photographic expression, sometimes sloppiness and / or accident can lead to an interesting result. It's possible to be playful.

This is getting off-topic, though. Note that I did say above:

But with a production schedule, artificial light can be handy. (1) It can be summoned to order. (2) Unlike daylight, it's predictable (can be managed).

 

[Birdy06]

I suppose, if you have the luxury of waiting for a bright/overcast/dry day... you do live in the UK don't you?

There’s plenty of days available when it’s overcast and bright enough to use in the UK. As I mentioned, I tend to photograph my own work in batches at some point prior to an exhibition, mostly for my own records. It’s not difficult or onerous to wait for a suitable day to do so. If I have to photograph work ‘urgently’ and it’s not suitable, I’ll just use the low tech daylight strip lighting and daylight bulbs in my studio. It’s definitely not totally suitable compared to professional lighting but with a little tweaking it works fine. I usually have to do a little work in Photoshop but nothing that adds a great deal of time. At some point in the future, I may look into getting a better setup, it depends if I want to go further down the print route (which I probably won’t).

 

[simonbarker]

It’s not difficult or onerous to wait for a suitable day to do so.

That's not what they're talking about, you're referring to having the right quantity of light whereas they're talking about having the right quality of light.

 

[Birdy06]

That's not what they're talking about, you're referring to having the right quantity of light whereas they're talking about having the right quality of light.

So is natural light not suitable or of suitable quality? I’m not being flippant by the way. I appreciate there is a good amount of technical know how involved with studio lighting and wasn’t trying to diminish its importance.

 

[HoppyUK]

You're in a feisty mood today. Obvious? Low-brow?

<snip>

Sorry about that Rog, but I really think that statements like 'daylight is best for everything' cannot be left unchallenged, and since this is the Lighting forum it's unlikely that they won't be

 

[sk66]

So is natural light not suitable or of suitable quality? I’m not being flippant by the way. I appreciate there is a good amount of technical know how involved with studio lighting and wasn’t trying to diminish its importance.

There's certainly a difference between minimally suitable for purpose and price versus optimal (or as close as can be achieved).

it depends if I want to go further down the print route (which I probably won’t).

If you're trying to sell prints (photos) of your paintings, then more optimal photos should result in better sales... but it begs the question as to whether the costs (time/expense) is justified by the benefits (increased sales/prices).

 

[HoppyUK]

So is natural light not suitable or of suitable quality? I’m not being flippant by the way. I appreciate there is a good amount of technical know how involved with studio lighting and wasn’t trying to diminish its importance.

Not at all. Daylight often is perfectly suitable for copying, though of course it's highly variable and unpredictable. Used it myself when the subject and situation are well matched though TBH that's usually because it's easy and 'good enough'. But it's very often not suitable or at least some considerable way from optimum and that also applies to general picture taking even when a lot of the time it's hard to do much or even anything about it eg landscape.

This is drifting a bit off-topic, but I often think that most people would be better off not buying an extra lens but instead investing a small amount of money and some time in a decent flash gun and learning how to really use it. That'll not only improve many of their pictures, but it will dramatically transform some of them, indoors and out.

Edit: 'photography' literally means 'drawing with light' (from the Greek)

 

[Garry Edwards]

So is natural light not suitable or of suitable quality? I’m not being flippant by the way. I appreciate there is a good amount of technical know how involved with studio lighting and wasn’t trying to diminish its importance.

OK, if it's a serious question then I'll try to give a serious answer.
What we want it an even light source, positioned above and to one side of the (flat) subject, at an angle of circa 45 degrees. This will light one side and because the angle of reflectance equals the angle of incidence the specular highlights and the shadows will be controlled, showing brush marks etc but not allowing them to dominate, and controlling reflections.
Then, we duplicate this effect from the other side, ending up with balanced lighting.
The easiest way of doing this is to use two identical softboxes, fitted to identical flash heads, which are attached to identical light stands.

Daylight can be fine for this, as long as we can control it's direction, and to do this properly the obvious approach is to choose a cloudy day, so that they whole sky becomes a huge softbox. Bright sun won't do it because it will create obvious unwanted reflections. And regardless of the colour temperature of the sunlight at any given moment, it needs to be consistent too - it won't work with a blue sky on one side and a red sky on the other.

And we can't have any light coming from 90 degrees, bouncing straight back up at the lens, no amount of polarisation can overcome the inevitable reflections in that scenario, so as we (unfortunately) only have one sun on this planet we need to introduce a bluudy great black flag that blocks out the sun from the centre of the image. This should be theorectically achievable with just a few days of work, but it's just easier to use flash heads in softboxes.

That's the long answer. The short answer is that many types of natural light would be fine, if only we could control its direction, harshness, colour and consistency, but the simple fact of the matter is that we can't, so we take the simple option of using the much more consistent resource of artifical light and the excellent, cheap tools that we have to control and modify the direction and reflective qualities.

Another answer is that lazy people may use daylight to avoid having to think it all through, but really lazy people just use artificial light to avoid the problems caused by natural light and to achieve the best possible results with a minimum of time, effort and so on.

There’s plenty of days available when it’s overcast and bright enough to use in the UK. As I mentioned, I tend to photograph my own work in batches at some point prior to an exhibition, mostly for my own records. It’s not difficult or onerous to wait for a suitable day to do so. If I have to photograph work ‘urgently’ and it’s not suitable, I’ll just use the low tech daylight strip lighting and daylight bulbs in my studio. It’s definitely not totally suitable compared to professional lighting but with a little tweaking it works fine. I usually have to do a little work in Photoshop but nothing that adds a great deal of time. At some point in the future, I may look into getting a better setup, it depends if I want to go further down the print route (which I probably won’t).

No. You're using discontinuous spectrum light sources that cannot reproduce all colours correctly. There is no "tweaking" that can correct this, all that can be done is to mitigate it.
Hope this helps.

 

[Birdy06]

OK, if it's a serious question then I'll try to give a serious answer.
What we want it an even light source, positioned above and to one side of the (flat) subject, at an angle of circa 45 degrees. This will light one side and because the angle of reflectance equals the angle of incidence the specular highlights and the shadows will be controlled, showing brush marks etc but not allowing them to dominate, and controlling reflections.
Then, we duplicate this effect from the other side, ending up with balanced lighting.
The easiest way of doing this is to use two identical softboxes, fitted to identical flash heads, which are attached to identical light stands.

Daylight can be fine for this, as long as we can control it's direction, and to do this properly the obvious approach is to choose a cloudy day, so that they whole sky becomes a huge softbox. Bright sun won't do it because it will create obvious unwanted reflections. And regardless of the colour temperature of the sunlight at any given moment, it needs to be consistent too - it won't work with a blue sky on one side and a red sky on the other.

And we can't have any light coming from 90 degrees, bouncing straight back up at the lens, no amount of polarisation can overcome the inevitable reflections in that scenario, so as we (unfortunately) only have one sun on this planet we need to introduce a bluudy great black flag that blocks out the sun from the centre of the image. This should be theorectically achievable with just a few days of work, but it's just easier to use flash heads in softboxes.

That's the long answer. The short answer is that many types of natural light would be fine, if only we could control its direction, harshness, colour and consistency, but the simple fact of the matter is that we can't, so we take the simple option of using the much more consistent resource of artifical light and the excellent, cheap tools that we have to control and modify the direction and reflective qualities.

Another answer is that lazy people may use daylight to avoid having to think it all through, but really lazy people just use artificial light to avoid the problems caused by natural light and to achieve the best possible results with a minimum of time, effort and so on.

No. You're using discontinuous spectrum light sources that cannot reproduce all colours correctly. There is no "tweaking" that can correct this, all that can be done is to mitigate it.
Hope this helps.

Thanks for the reply and others above. I do seem to have sidetracked the OPs thread, apologies! I have taken hundreds of images of paintings and whilst the setup (ie just using diffused daylight outdoors) isn’t ideal it has worked absolutely fine for the requirements of print. I’ll definitely be following the thread for suggestions on studio lighting. It’s something which would probably make my workflow considerably easier.

 

[Richard King]

I've shot a lot of artwork

The cross lighting method is a good starting point

You want really even illumination, so getting your light sources distant really is helpful (ISL law) take time to check evenness of illumination with a flash meter across the whe area if a artwork

Write down your settings I.e the measurement of light hitng the canvas and what you shot at. The next shoot you do will likley be wanting the same settings. Repeatability is usually important, which is why you dont use natural light

Create a colour profile with an x-rite passport or similar

Your paper texture and media will determine how you handle the angle of your lighting. Even within brands of paper (Bockingford for example) there is a lot of variation in texture depth. You will likley be working with hard light, and fine tuning the angle to get the exact look you are wanting from the texture

If you are shooting oils, or more dimensional media, you may want to soften the lighting a touch to reduce hard shadows..

Keep an artwork as a reference that you always shoot at the start of each shoot to ensure consistency

Some specific pigments and paints are a bugger to get the colour right in camera. Windsor and Newton Cerulean Blue springs to mind. You do need to look at your whole shoot to output colour management process, to avoid getting tripped up. Sweat on the details and editing environment and understand that artworks are reflective and screens emit lught

 

[Richard King]

With regards to polarisation, even if the artwork is under glass, if you are lighting it properly, your camera will not record a reflection. Your lights will be bouncing off the glass away from the camera

The only thing you need to watch is what's behind the camera. Just whizz a black backdrop up behind the camera