[Marc Sabatella]

I have done it many times. Doesn't matter what you use, as long as it is neutral in color. Actually, you could probably deliberately use something a bit cooler than neutral if you wanted the resulting pictures to have a slightly warm cast (and vice versa).

[felix68]

All I use to do my custom white balance is my 18% grey card. I get a much better result consistently using the grey card than using something white.
So BBear, yes I have done it, many times and get better results setting white balance with a grey card than a white object. It works, try it yourself and you may be surprised at the accuracy.

[dkittle]

One thing that I noticed is that if your exposure is not correct, your custom whitebalance will be off.

I set up my softbox which is decided warm. I guessed at exposure settings, threw my grey card on the couch and snapped a frame for custom whitebalance. Low and behold, the image turned green (the temp turned out to be 3600 on that photo). I used my light meter and corrected my exposure and redid the custom whitebalance and it came out great, temp=5100.

Just something to keep in mind if you are working in manual and trying to set a custom white balance.

[Kerrowdown]

Aye my "pukka" Kodak grey card (real thing, must be true grey card then) has got a white back on it.

Kodak just think of every thing.

[SpecialK]

The K10D manual clearly states that a white object (eg. piece of paper) should be used for setting custom white-balance. I don't believe an 18% grey card will give correct results.

If the gray does not have a color cast, it will be fine. The camera does not know what white or gray (or black) is, anyway.

[Arpe]

One good thing about the K20D WB manua setting is that you can take a photo for the setting that isn't even all white (must have some white, or grey), then zoom in on the white bit and tell it to use that to balance - super duper idea.

[AndrewShirley]

I've been using an 18% Grey card for some time now and it works every time. The camera simply takes an RGB reading and calculates the difference between each of the channels then adds an adjustment to make them equal.

If you use a white card for custom white balance you run the risk of using an overexposed set of RGB values - each of which would simply be 255,255,255. Not accurate at all since your camera would then assume no adjustment is necessary and your WB is still off. Even if you clip one or two channels, a false WB adjustment will be made.

So, using the 18% Grey card gives very little risk of over/under exposure of the white-balance reading and therefore dependable results. Technically speaking you can use any card from black to white as long as its neutral.

Just my .02.

- Andrew