Ok, Hopefully this is a useful contribution for some people. It sure drove me nuts for a few days figuring it out !
White subjects on pure white backgrounds isn't as straight forward as one would hope....
I recently had a friend ask if I could shoot some chocolates she hand makes. She is in the process of making a brochure, being done by another friend who is a 'graphic designer' (don't know them - but use quotes because I'm not a 'photographer' either
). They have a requirement that she supply white background images, with preferably no shadow in them.. yawn.... Did I mention she makes lots of white chocolates
So after some discussion and earlier sample shots showing how boring it made her efforts look and what we could maybe do, she wants me to do some non-white background images for her upcoming website and personal/marketing use (yay! I get to play with a reason ..
) . But I did have to knock over this first request... so heres how I went about it.
I could have used a light tent, but there would still be shadows unless I nuked the whole scene and lost just as much fine detail...
.....or I could use some sort of shroud with a light diffuser in it. In fact, thats what I tried first. I butchered a cardboard box, cutting the sides at an angle and putting tracing paper over a center panel I removed. I then placed the chocolates on some rice paper under some clear acrylic. With some reflectors diligently placed around, and a flash shooting through the tracing paper at full power - heres the end result - not what I wanted!:
So some further research and questions and answers on some newsgroups, and here is the new approach - guaranteed to get you capturing white-on-white without loosing toooooo much definition in the white item.
The trick is to separate the background from the foreground, overexposing the background by 2 stops or more.
How do you do that if you dont have heaps of room, or a white wall handy ? You cheat of course!
Using some glass preferably, or failing that some clear acrylic (although beware, it behaves differently to glass slightly and requires a bit more 'futzing around' so to speak to get setup right as it transmits more light at shallower angle than glass which will bounce most of it at these angles). Get it supported high enough off of the ground, about a meter, meter and a half (3 - 4 feet for those imperial amongst us! ). I used two chairs turned back-to-back.
On the ground, place a white reflective card that is *flat* - preferably some corflute, or stiff card that is supported so it doesn't bow (I, when testing, used some card laid on another light stand as a 'backbone'). It needs to be flat to prevent spurious reflections, shadows appearing on it, causing flare and just general other hassles. Get it elevated to about a 30° angle towards the camera. Now this is the background you want to overexpose. Place a flash on the ground, and then with the camera in position on the tripod just behind it, place a Gobo extending to just underneath the subject.
Now take some shots and chimp it. Adjust the flash as necessary so that about two stops higher than you need the background is blowing out entirely, but the subject is still just a silhouette. Move it back and forth or up and down.. small adjustments can make a big difference especially when working macro. I was aiming for a working shot at F11, which meant I was looking for a sea of red at F13 (My logic being if they've blown at 13, by 16 it'll be about right...). Don't forget, if shooting Macro @ 250mm or something, you should zoom the flash so that you don't waste lots of that power throwing it way outside the frame.
In tonight's case, because of the angle I was shooting, I actually used a carefully ironed sheet as the reflector I overexposed due to the angle and the Sigma 70-300 Macro I was using.. the same angle using my Tammy though shoots clean through to the card/reflector diagrammed below... The "sheet on a wall" still works, but leads to throwing a lot of 'bounce' light onto the subject making it impossible to silhouette entirely - this results in the mild halo and nasty catchlights on the chocolates and lots of free 'fill light' that you may not want in the final product... but like I said.. I'm more interested in my ideas that aren't based on floating chocolates
Here is a crude diagram from a 'sideways' glance...
and a Lighting Diagram Diagram (if that makes sense) of the complete setup I used tonight - but only the flash under the flowers is relevant to over-exposing it for the pure-white:
With your subject now just a silhouette in a sea of blinking red (if you have highlights turned on in Playback
) - its just a matter of lighting it however you want! I ended up using a *lot* of lights in these captures - more because I deliberately kind of want to make these ugly
As you can see from the setup shots, all the dishes and ingredients are for tomorrow when I shoot some more varied compositions making them hopefully look more tasty
Here is my setup tonight - every light over a meter off the ground is personal choice based on the subject: 
A wider view, chocolates at the ready (I hadn't picked out the 'heros' yet ): 
And all the supplies ready to go on the kitchen table for the next round. I plan to do the chocs with their filling ingredients on dishes in better compositions - hence the nuts, peanut butter, chocolate to grate up for effect, etc... 
And with all that, I produced some images like these - not the greatest compositionally or by any means great lighting - but they ARE what I wanted.
The only PP is a v.light denoise and some sharpening ( you can tell I know!
) -
But it is white-on-white with no shadows! 
And to show it works just as good on non-white-on-white: 
(theres some more on my flickr page
Chocolates II - a set on Flickr)
I hope this helps anyone else that needs to shoot white-on-white at any stage!
But...
Do remember to shoot a grey-card or otherwise white balance stuff properly and switch to custom - all that white can drive the AWB a little screwy and its a PITA to fix - go on - ask me how I know
..
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