Background
Numerous materials and processes have been proposed for use as white standards. These include smoked magnesium oxide and polytetrafluoroethylene or PTFE. Both of these materials have significant drawbacks in environmental safety and complexity of preparation and disposal. The proposed white standard is shown in Figure 1 next to a freshly pressed PTFE or halon disk. Aside from the irregular border, the size, shape and general appearance of the proposed white standard greatly resemble that of the freshly pressed halon disk. The average cost of the white standard material is less than US$0.10 each in quantity. Bulk quantities of pre-packaged standards are also widely available through a number of distribution channels.

Figure 1. Pressed halon (left) compared to the proposed new white standard (right).

Optical Properties
The reflectance data for the proposed white standard at 25ºC are presented in Figure 2. This graph shows the reflectance of the standard relative to other commonly used white standards. This includes NPL calibrated Spectralon, freshly pressed PTFE, the white from the Macbeth chart, the white BCRA-NPL Series II tile (CCS II), and the white patch in the JOBO test chart. There is slight dip in the reflectance curve below 500 nanometers but as the results in Figure 3 show this is not a significant deviation for many applications. The goniophotometric properties, not shown here, are also quite good with a suprisingly nearly Lambertian bidirectional reflectance function. Finally, one of the hardest problems with calibrations targets is thermochromism, especially in ecological laboratories with a wide temperature excursion. To address this it has been proposed that polydiacetylene polymers may be formulated to provide compositions having numerous chromic transitions triggered by temperature changes. As explained in paragraph 9 of that invention, the reference white turns visibly blue when the temperature is below threshold.

Figure 2. Reflectance curves for a number of white relectance standards, including the newly proposed standard shown as a solid black line.

Camera White Balance
As one compelling example of this new white standard consider the challenege of white balance for digital phtography. An incorrect white point often results in a strong color cast as is shown in the top portion of Figure 3. The widespread availability of the proposed white reflectance standard can then be used with the manual white balance mode of the camera to capture a color corrected image, shown on the bottom of Figure 3. The white standard, shown between the pine cone and the slotted spoon, was used as the white region before the image was captured. The result is a dramatic improvement.

Figure 3. Before (above) and after (below) correction of a scene for an incorrect white balance using the proposed white standard.

Preparation
The proposed white reference material consists of a soft circular white material sandwiched between two black protective layers. The ideal preparation of the white standard is the removal of one of the hard layers, exposing the soft middle layer. In general a gentle, twisting motion is most effective. Care must be taken to avoid tearing or separating the white material from the protective base layer. Once one of the hard outer layers has been removed, any residual protective material should be removed using tweezers or a gentle brushing with a camel hair brush. Due the fragile nature of the material, compressed air should not be used to clean the standard. In practice the most dangerous substance is acetone, because it is widely used for cleaning purposes. Acetone will destroy the calibration target.

Figure 4. Removal of one of the two protective transport layers to reveal the white relectance layer using a quick, smooth twisting action.

Disposal
Once the standard has reached the end of its useful lifetime, it must be disposed of. This is one of the key strengths of this standard in that the disposal is achieved by ingestion. There may be variation in the exact number of standards that can be disposed of at once, but current experiments by the authors show that up to five white standards can easily be disposed of at once while other sources have shown that this number could be as high as seven. This is fairly close to the 51 gram manufacturer recommended serving size. The targets are suitable for use in compost piles or can be given to children.

Conclusions
Happy April Fool's Day! The data are real, as are the results shown in Figure 3 but this post is intended to be humorous. Yes that's an Oreo(tm) cookie in Figure 4 ;) Nathan and Giordano would like to thank Tim, Kevin and Seth for their contributions to this post. We have to admit we were quite pleased with the results for the camera cookie white balancing or CWB and plan more testing. When our fadeometer gets here we'll also have to see if we can sneak some cookies in.