White Balance - How is plastic made white? RGB(255,255,255)

Question

Yes, it is a photography question, but it requests a chemist answer. Overall concern is about the neutral color accuracy of White Balance cards that are white. It can be a purchase and a usage question, about photographic white balance cards.

OK, stated as one question: How is white plastic made to be white, specifically is it automatically and accurately a neutral color tint?

Regarding inexpensive white plastic White Balance Cards.. How are they made to be neutral white? Not asking details of plastic manufacture, but is the color white always naturally and accurately neutral? Does this white neutral color accuracy need control steps? Other than by adding pigment, might it come out a bit tinted, less neutral?

Some white balance cards are light gray color, which requires mixing in pigments, which is a complication then requiring control and checking for accurate neutral color. Other plastic just seems to be white already.

I know there are many plastics, which is not the question. Some are clear color, some have added color. Some are white? Asking about white.

Some plastics (like say PVC pipe) are white (I think). Is it natural? Is it neutral? In general, how is the accuracy of being neutral white (no color cast) controlled? Is color control necessary? If control, what might be acceptable specifications?

The question is, is there a concern about accurate neutral color of inexpensive white White Balance cards for photography? In practice for White Balance, it seems very close. How close is white plastic to known neutral? Is it assured? Any clue appreciated.

Answer 1

This question is dificult to answer. But my short answer is no.

Do not trust all plastics to be white at all.

Do not trust glossy plastics.

Do not trust transluscent plastics.

It is dificult because it is a case by case answer. It can not be answered inclusive by generic answers, for example pvc pipes of diferent brands have noticable diferences.

Some styrene I have shooted has a very noticable magenta tint, some formaica has a blue tint.

Plastic can be afected by age, solar exposure, oxidation which can give a warm tint.

Inclusive the nylon used in softboxes can turn yellowish in time.

The main concern for a plastic manufacturer im sure is cost-benefit-properties (Temperature and solvent resistance, degradation, translucency, etc). Some of them sure, are meant to look white enough, but I supose NO one takes into an account that some photographer will see the perfect white balance of a plastic to be used as a background or white card.

So the answer is no.

If you are looking for a cheap white bananced card I supose they have a minimum quality to offer somehow neutral white. Probably they have a white paint coating. Paint is more likely controlled to be white. One main purpose of paint is to be somehow acurate in color.

If you want a cheap option you probably could go for a high quality inkjet bright paper. I would trust more on this paper than almost any plastic.

---

P.S. There is no white 255,255,255. That is a blowned white. Almost all colors on the planet will give you that color if you leave your shutter open long enough.

Answer 2

Photo scientists use instrumentation to calibrate film and photographic prints. These instruments are called densitometers. Transmission densitometers direct a beam of light of known intensity at a film sample. The light transverses the film and the intensity measured. Transmission is the amount of light that gets through divided by the total amount of light that hits. Transmission is labeled “T” and is expressed as a percent Opacity is the total amount of light that hits divided by the amount that gets trough. Opacity is labeled “O” and is expressed as a decimal fraction to avoid confusion. The density of the material is labeled “D” it’s “0” stated as a logarithm (base 10).

A reflection densitometer is used to measure opaque surfaces. These were initially used to measure photographic paper however they are in wide use in other disciplines especially lithography, and paint manufacturing and matching. These instruments project a light of know intensity and measure the light after it has been reflected.

Specifications for both transmission and reflection densitometry are maintained by the International Standards Origination (ISO). The intensity and color output of the lamp are specified. The lamp output is filtered. Neutral test targets are filtered using a Wratten 106 ambler filter. This filter adjusts the instruments response so that it matches the now outdated S-4 photocell (the standard that matches the response of the human eye).

Colored subjects are measured taking three readings. These are filtered with Wratten 98 blue, Wratten 99 green, and Wratten 92 red. Note: Wratten filters set the standard. Made by the master filter maker Frederick Wratten, at the English Firm of Watten and Wainwright, purchased by Kodak 1912, The catalog numbers maintained to honor Wratten.

A pure white target would measure 0 Red 0 Green 0 Blue refection densitometer. The 18% gray target gray card measures 0.75 R 0.75 G 0.75 B. All well studied and well documented. If the target is neutral in color, all three values are the same.

Answer 3

Plastic is usually made white with titanium dioxide, but not all. For example the aforementioned styrofoam is white because of gaseous bubbles, just like shaving cream. One thing to consider is that the raw polymer is not always absolutely perfectly colorless etc.