with different
threshold temperatures were obtained and mixed. The same approach was used as in
Thermochromic Silicone
project; epoxy resin was used as the binder here.
Hot tea is hot. Tongue-testing is not advised. Reaching for the cup and realizing it is still too hot is rather annoying. A visual test is more desirable.
Three microencapsulated leuco-dye thermochromic pigments with different
threshold temperatures were obtained and mixed. The same approach was used as in
Thermochromic Silicone project; epoxy resin was used as the binder here.
The pigments used were:
|
Tea mug test with hot water |
Tea cup test with hot water |
Tea mug test with hot tea |
|
|
Water faucet test - cold to hot, hot to cold |
Water faucet test |
Water faucet test |
The beverage consumption vessels have the indicator strips on both the inside and the outside. The inside strip has immediate reaction to the liquid, the reaction of the outer strip is significantly delayed by the heat transfer through the vessel wall.
Practical tests shown that the inner strip is difficult to see when the beverage has significant color or opacity. The process hassle may not be worth the immediate reaction; the delayed reaction of the outer strip is fully sufficient.
The tea can be just about consumed when the indicator strip turns red. The temperature is nice when the strip starts showing hints of purple.
 Mug, finished |  Mug, finished |  Mug, finished |  Mug, with hot tea, fresh-poured |
 Mug, with hot tea |  Mug, with hot tea |  Mug, with colder tea, drink-ready |
 Cups, mug and spoon, ambient |  Cups, mug and spoon, hot water |  Cups, mug and spoon, hot water |  Cups, mug and spoon, hot water |
 Mug and spoon, hot water |  Cups and mug, hot water |  Cups and mug, hot water |
The spoon requires a thicker layer of the pigment or higher pigment loading of the mix, to provide higher contrast between the color changes. The underlying bright white layer can overpower the color during photography, especially with flash.
 Spoon, cold |  Spoon, hot tea |  Spoon, hot tea |  Spoon, hot tea |
The teamaker allows visual checking of function at a glance.
 Teamaker, cold |  Teamaker, hot |
The faucets now provide visual temperature feedback, so the user now can avoid touching water that is uncomfortably hot or uncomfortably cold.
 Faucet, cold |  Faucet, cold |  Faucet, hot |  Faucet, hot |
A food-compatible resin was desired. A CHS-1200 kind of epoxy resin was chosen on the basis
of availability, with the P11 hardener (triethylenetetramine). While not food-grade on its own,
it can be made compatible by washing the unreacted hardener out of the resin matrix with repeated
washing with water and then with 3% solution of citric acid.
The pigment was mixed with a small batch of resin, to test compatibility. Degradation of function was not observed in the scale of over a week.
 Raw pigment and epoxy before mixing |
The thermochromic composite ("active mix") is translucent.
A mixture of the resin with a titanium dioxide pigment, food-grade anatase, Pretiox AV-01-FG,
was used as a bright white background ("white mix") where the underlying material was not white. This mixture has
high cover capability.
A clear resin without additives was used where necessary as a topcoat.
Mixes of the white pigment with the thermochromic one yield muted pastel colors, with better covering uniformity but much less evident color changes.
The resin used has fairly high viscosity, interfering with the smooth spreading. The viscosity can be significantly lowered by heating, e.g. with a hairdryer. The presence of the thermochrome allows easy visual control of the heating progress and level.
Adhesive tape was used for masking the background, for delineating the shape. This was chosen over direct shape painting due to better ability to achieve sharp straight lines.
The resin mix was painted over the masked area and let cure. When it was not runny anymore but still not fully hardened, the tape was removed; a hairdryer was used to heat the object, to melt the adhesive. There was considerable amount of leftover adhesive; after full curing of the epoxy this was removed with acetone.
With the clearcoat, the tape was removed while the resin was still somewhat runny. This, followed with a hairdryer heating, formed a smooth edge; later removal of the tape tended to yield sharp rectangular edge.
Later removal of the tape, when the resin is more cured, may require careful cutting through the resin layer along the edge of the tape.
Several objects were chosen as test ones.
A pair of china tea cups and a larger tea mug were used for the drinkware. The white background allowed direct application of the active mix, followed with a topcoat to protect the active mix layer, and prevent direct food contact with the safety-unrated pigment.
 Cup with tape masks |  Cup with tape masks |  Cup with tape masks |  Cup with tape masks |
 Mug with tape masks |  Mug with tape masks |  Mug with tape masks |  Mug with tape masks |
 Cup with active pigment over mask |  Cup with active pigment over mask |  Mug with active pigment over mask |  Mug with active pigment over mask |
 Mug with active pigment over mask |  Mug, with mask and active pigment |  Mug, with mask and active pigment |  Cup, with mask and active pigment |
 Mug, mask for transparent overcoat |  Mug, mask for transparent overcoat |  Mug, mask for transparent overcoat |  Cup, mask for transparent overcoat |
 Cup, mask for transparent overcoat |  Cups, mask for transparent overcoat |
A teaspoon was selected for a removable test object that can be placed to the beverage at will. A white mix was used as the undercoat on a slightly abraded stainless steel, followed by a layer of the active mix and then by the topcoat.
 Spoon, prepared |  Spoon, prepared |  Spoon with white backcoat |
An electric kettle and a percolation teamaker were chosen as larger objects. The kettle is white, so it got only the active mix. The percolator got a strip of white mix on the glass vessel, and the active mix strip.
 Kettle with tape mask |  Kettle with tape mask |  Teamaker with tape mask |  Teamaker with tape mask |
 Teamaker with tape mask |  Teamaker with white backcoat |  Teamaker with white backcoat |  Teamaker, tape mask over white backcoat |
 Kettle with active pigment over mask | Teamaker, mask removed |  Teamaker, mask removed |  Teamaker, mask removed |
Teamaker, hot |
A pair of water faucets, one in the bathtub and one on the washbowl, served as other set of test objects. They got a strip of white mix, a thick high-contrast strip of active mix, and then a topcoat to protect the layers from damage during cleaning.
 Faucet 1 with tape mask |  Faucet 1 with white backcoat on mask |  Faucet 1, tape mask over white backcoat |  Faucet 1, mask removed, traces of adhesive |
 Faucet 2 with tape mask |  Faucet 2 with white backcoat on mask |  Faucet 2, tape mask over white backcoat |  Faucet 2, mask removed, traces of adhesive |
The epoxy sometimes suffers from adhesion failure. This is more likely to happen after the acid wash; the hypothesis is that the unreacted hardener gets washed out, which makes the topmost layer slightly contract and put the interface layer in tension.
This occured with the inner layers of both cups and the mug. A second attempt was assisted with abrasion of the smooth glaze with a diamond burr; this improved the adhesion, though one of the inner strips of the mug detached later as well.
The adhesion failure was also encountered with the spoon; this occurred during eating of an ice cream. The thermal shock may have worsened the interfacial tensions.
 Detached strips |  Detached strips |