Metamerism, and why a foundation matches indoors and not outside

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Researched. We have not used this one long enough to give you a verdict, and we would rather say so than invent one. What follows is how it works, who it suits, and what it will not do. When we have used it properly, this page carries the verdict and the date.

L'Oréal Paris True Match Super-Blendable Foundation

There is a word for what has happened, and it is more useful than any shade-matching tip: metamerism.

Two colours are metameric when they look identical under one light and different under another. This is not a trick of memory or a failure of attention. It is a measurable property of the two surfaces, and it is the reason a foundation can vanish into your jaw under the counter lights and read like a mask in the car park outside.

The boring mechanism

Skin gets its colour from a short list of things: melanin in the upper layers, haemoglobin in the blood underneath, a little carotenoid, and the way light scatters as it passes through and comes back out.

Foundation gets its colour from iron oxides — red, yellow, black — plus titanium dioxide for opacity and sometimes ultramarine for a cool cast.

Those are entirely different materials, and they reflect light in entirely different patterns across the spectrum. So when a foundation "matches" your skin, the two surfaces are not reflecting the same light. They are reflecting different light in a way that happens to add up to the same appearance under whatever illuminant you were standing in.

Change the illuminant and the sums stop agreeing.

This is not sloppy manufacturing. It is unavoidable. A match that held under every light would need the foundation to be made of the same things your face is made of.

Why a shop is the worst place to do this

Two problems, and they compound.

The first is the spectrum. Warm LED and incandescent lighting is heavy at the long wavelengths and thin at the short end, so it flatters anything with red and yellow in it. Daylight is broad and even and carries far more blue. A shade that reads neutral under a warm bulb often reads orange outdoors, because outdoors is the first time the blue end of it has been asked to do anything.

The second is direction. Shop lighting is usually a point source above your head, which is the most forgiving angle there is. Daylight is enormous and diffuse and arrives from everywhere, including from below off the pavement. It finds edges. A jawline that looked seamless under a downlight is a visible line in a doorway.

There is a number for the first problem — the colour rendering index, or CRI, which scores how faithfully a light source renders colour against a reference. You will not find it printed anywhere near the testers. Assume the worst.

The two axes people confuse

Depth is how light or dark the shade is. It is easy to see and most people get it roughly right.

Undertone is the hue sitting underneath: the warm yellow-to-golden range, the cool pink-to-red range, and the neutral ground between. It is harder to see, and it is the one that goes wrong.

The three-bucket system is a simplification, and the skin that most often falls through it is olive — a green-grey cast that gets filed as "warm" on the grounds that it is not pink, and then reads orange the moment it is on a face.

A shade can be correct on depth and wrong on undertone. That is the one that looked fine in the mirror and looks grey in a photograph.

The other reason, which is not the light

Foundation that matched at the counter and is a shade darker by lunchtime is usually described as oxidising.

Whatever the exact cause — pigment settling into skin oil, the vehicle evaporating and concentrating what is left behind, or something in the formula genuinely reacting with air — the practical rule is the same and it is dull. Judge a shade at twenty to thirty minutes, not at thirty seconds. Almost nobody does this, which is why the shade that seemed obviously right in the shop is the one now sitting unused in a drawer.

Flashback, which is a third thing entirely

If the problem only appears in photographs taken with a flash, that is neither metamerism nor oxidation.

Titanium dioxide and zinc oxide are extremely good at bouncing light straight back towards its source. In daylight this is invisible. Fire a flash at it from a foot away and the camera sees a pale disc where your face was. Foundations carrying SPF are the usual culprits, because a mineral filter is a great deal of titanium dioxide by definition.

The regulatory bit worth knowing

In the United States, colour additives are the most tightly controlled part of a cosmetic. Each one must be approved by the FDA for its specific use, and a subset must be certified batch by batch. Iron oxides — which are doing nearly all the work in your foundation — sit on the exempt-from-certification list.

We mention it because it takes some heat out of the shade-range argument. Almost every foundation on the shelf is mixed from the same small box of pigments. A brand with forty shades and a brand with twelve are not working from different palettes. They have made different decisions about how finely to divide the same one, and that decision costs money rather than requiring invention.

The test that costs nothing

Three shades, striped along the jaw and running down onto the neck. Not the back of the hand, which is a different colour from your face and always has been.

Then walk to a window, or better, outside. Look without a mirror lit from the front. Wait the twenty minutes. Photograph it in daylight if you want a record, but know that your phone is white-balancing the whole scene and will quietly correct away some of what you are trying to see.

What no foundation will do

• It will not correct for the light you are standing in. Nothing does.
• It will not become right by being blended harder. A wrong undertone blended well is a wrong undertone spread across more of your face.
• It will not match your hand, your chest and your jaw at once, because those are three different colours.

The one thing that decides whether this works

Match in the light you are actually seen in.

If your days are spent under office strip lighting, that is the light your face lives in, and that is where the match has to hold. For most people the answer is daylight, because daylight is the least forgiving and it turns up every day whether you were ready for it or not.

And if the reason you want foundation at all is that the tone underneath is uneven rather than that you enjoy wearing it, that is a different problem with a different answer, and what "brightening" actually means is the more useful page.

The product

Its entire organising principle is the undertone axis: every shade is labelled cool, neutral or warm with a depth number after it, which is more information than most ranges bother to print. It has been on shelves for over twenty years and it is cheap enough that getting it wrong once is a lesson rather than a loss.

The one people are searching for is the L'Oréal Paris True Match Super-Blendable Foundation.

L'Oréal Paris True Match Super-Blendable Foundation

We do not print prices here, because a price we typed last month is a price that is wrong today.

Written by JamieG in Garner Town, Tennessee.