Is there any kind of thermochromic material and/or paint that is capable of changing its color in the range from 4-8°C (39-46°F)? I'm trying to paint a glass bottle and want a visual aid for its temperature.
I found a supplier of raw thermochromic pigment active in the temperature range you are looking for. But to make it into paint you would have to add binder yourself.
Company is called Shenzhen Yu Mingjie Pigments Co., Ltd.
Has different thermochromic pigments active in the ranges -5C to 78C
Be sure to specify the temperature range you are interested in.
From this web site for Hallcrest is the following excerpt:
Hallcrest thermochromic formulations are available as a pigment or a liquid crystal screen ink. Colors and temperatures can be customized to your application and printing capability. Thermochromic Temperature Range: -10ºC to 69ºC (14ºF to 156ºF)
They have standard activation temperatures of 15°C, 31°C and 47°C, and offer special activation temperatures in the range of -10°C to 69°C.
For email and telephone go to this site.