Interference optics, batch matching & photography
Five things that are unusual about a color with no pigment.
Iridescence comes from a film thin enough that light reflecting off its two surfaces interferes with itself, so the color you see depends on film thickness and on the angle you look from. There is no pigment. That makes approval, batch matching and even product photography behave differently from any other finish in the category.
The color comes from thickness, measured in nanometers
A thin transparent film reflects light from both its surfaces, and those two reflections interfere constructively or destructively depending on wavelength, thickness and angle. Change the deposited thickness slightly and the whole sequence of colors shifts. It is the same physics as an oil film on water, applied deliberately and controlled to a tolerance.
There is no single shade to approve
Standard color approval compares a sample against a reference under defined lighting, and that method fails here because the color changes as the sample is turned. Approval works instead by agreeing a pair of physical limit samples and a viewing protocol — the same angle, the same light — and accepting the range between them.
Batch variation shows as a different rainbow, not a different shade
When deposition drifts, the effect is not that the vessel is slightly bluer but that the sequence of colors across the surface has moved. Customers who have bought before notice, because they compare against the object in their hand. Tight process control matters more here than on a pigmented finish where a small shift is barely visible.
Photography almost always misleads
A camera fixes one angle and one light source, so a product shot shows one slice of a finish that exists as a range. Customers regularly report that the object does not match the picture when both are correct. Showing two or three angles, or a short video, prevents a return that would otherwise be entirely avoidable.
The film still has to survive a candle
Whatever the optics, it remains a coating on the outside of a vessel that will be heated from the inside along a traveling wax line. Adhesion and appearance are assessed by burning filled units to the base, because a film thin enough to produce interference is also thin enough to craze in a way that changes the color.
The effect depends on the angle it is viewed from, so the sample must be handled
An interference film changes color as the eye moves, which means a flat photograph or a single fixed view describes almost nothing about the finished product. Approval is done by turning a physical sample under the lighting the product will be sold in.
