Quite a number of years ago, I made my own white card. It is basically made up by two white access cards in plastic glued together and sanded down so that they have a matte finish.
The cards have been good enough for my meager use, I'm purely an amateur and hobby photographer, and though I knew that the card was almost certainly not pure white or a good balance, it has served me well.
However now I've finally purchased a white/gray card, and I'm wondering if I can still use the white card that I made, since it has a size that is a bit easier to carry around, and I have attached a strap to it so that I can carry it around my neck or wrist more easily.
The question is this:
If I take a photo, now, of my new real white card, alongside the one of my own creation, can I figure out the difference, so that if I keep using my old card, I can adjust white balance to it, and then apply an additional fixed adjustment to bring it into correct white?
Or, will the amount to adjust by not be fixed, but say vary depending on the light?
Or should I just throw it away altogether and forget I ever mentioned it? :)
Here's a Canon EOS 60D RAW file I just took. This is indoor lighting, so quite yellowish, but when I take a white balance reading from the small card and the large card, close together, they're off by about 50 give or take.
The homemade card is darker, but the difference which I originally took as a difference in tint, appears to be more about the brightness than about color.
IMG_0962.cr2 - About 21-22MB.
This tells me that it's not too shabby the card I made myself, so I can apparently keep using it.
To answer implied questions from the current answer:
- No, I'm not doing any product or production photography, this is purely for my own enjoyment
- Yes, I'm using RAW, and only RAW