Measuring Shade and Opacity
Tape/reflectivity test:
The Novo-Shade Duo + uses reflectance to grade a surface colour from pure white (100% Reflectance) to Black (0% Reflectance). This simple colour grading is effective in measuring the cleanliness of steel.
Equipment
Clear “Scotch” or 3M tape.
Rhopoint Instruments Novo-Shade Duo 0/45° Reflectometer operating in “Shade Mode”
Test procedure
Stick a piece of clean uncontaminated tape onto a sheet of white copier type paper. This is the 100% reflectance sample (A).
Stick a new piece of uncontaminated tape (B) onto the metal surface to be tested, press and smooth the tape so any contaminates are stuck to it. Carefully peel the tape from the surface and transfer it, sticking it to the same piece of paper with 100% reflectance sample.
Measurement
Calibrate the Novo-Shade Duo + on the clean white tape (A)
The average reflectance value of several readings should be taken across the contaminated area on tape (B). A minimum of five is recommended; use the statistical analysis function to ascertain this value. The average value indicates cleanliness; a clean surface will exhibit higher reflectance.
Can the Novo-Shade Duo replace a cryptometer?
The Novo-Shade Duo + does a better job than this, however, it can only be used to measure dried/cured films.
Dry film hiding power is more important than wet film hiding power – the paint may cover the surface when wet but could exhibit show-through when cured.
Method
The customer draws down the paint on an opacity chart using a standard draw down method. It is sensible to draw down a master vs batch.
The customer allows the paint to cure and uses the instrument in opacity mode- measuring 3 times on white and then 3 times on the black portions of the chart.
Hiding power is automatically calculated. The hiding power of the master and batch are compared.
Advantages
This is an objective measurement- a % hiding power is given (not a subjective judgement).
It can be used for all coatings and draw down methods- as long as they can be done on an opacity chart- print proofing, draw down, K-bar, brush out etc.
The hiding power of inks printed onto transparent media can be measured by placing the printed material over black and white tiles.
Any colour paint/coating can be measured.
The cured drawdown can be filed as QA evidence.
Wet film hiding power and Dry film hiding power are not equivalent and the latter is most important to the customer!
Some high/low viscosity paints/coatings can not be measured on the cryptometer.
