The concept of emissivity has been with the scientific and engineering world since Planck formulated his blackbody radiation law more than a century ago. Nevertheless, emissivity is an elusive concept even for experts. It is a vague and fuzzy concept for the wider community of engineers. The importance of remote sensing of temperature by measuring IR radiation has been recognized in a wide range of industrial, medical, and environmental uses. One of the major sources of errors in IR radiometry is the emissivity of the surface being measured. In real experiments, emissivity may be influenced by many factors: surface texture, spectral properties, oxidation, and aging of surfaces. While commercial blackbodies are prevalent, the much-needed grey bodies with a known emissivity, are unavailable. This study describes how to achieve a calibrated and stable emissivity with a blackbody, a perforated screen, and a reliable and linear novel IR thermal sensor, 18 dubbed TMOS. The Digital TMOS is now a low-cost commercial product, it requires low power, and it has a small form factor. The methodology is based on two-color measurements, with two different optical filters, with selected wavelengths conforming to the grey body definition of the use case under study. With a photochemically etched perforated screen, the effective emissivity of the screen is simply the hole density area of the surface area that emits according to the blackbody temperature radiation. The concept is illustrated with ray tracing simulations, which demonstrate the approach. Measured results are reported.