Leading on from a residency in the Laboratory in Spokane, WA, I was keen to reopen my research into thermochromic inks. It was something that I had only just begun to explore in this two-month residency but had had promising results. The details of this can be found in an old blog post here.
THERMOCHROMICS
Thermochromics are inks that change colour due to a change in temperature, similar to mood rings. One of the best suppliers of Thermochromics is SFXC. In fact, they make fantastic inks of all colours and can be found in the list of suppliers.
One of the issues I had discovered is that they do not mix or work well with oil-based inks, which removed all types of relief and intaglio printmaking from the process. The second restriction was, with the powder pigments, it is difficult to get and ink thick and opaque enough to cover the image underneath fully. This only worked with a very heavy and thick black pigment.
You can also find thermochromic inks that change at higher or lower temperatures, making it enjoyable to combine them and get a rainbow or mood ring effect as the temperature increases.
HEATING CIRCUITS
One of the goals of this research has been to create a heating circuit that is strong enough to change the colour of the inks. When an electrical current travels through a wire, there is always a small amount of heat created. This can be manipulated by putting a high wattage through a material with high resistance. The science of this can be found here: When current flows through a conductor, heat energy is generated in the conductor. The heating effect of an electric current depends on three factors:
The resistance, R of the conductor. A higher resistance produces more heat.
The time, t for which current flows. The longer the time the larger the amount of heat produced. The amount of current, I. the higher the current, the larger the amount of heat generated.
Hence the heating effect produced by an electric current, I through a conductor of resistance, R for a time, t is given by H = I2Rt. This equation is called the Joule’s equation of electrical heating.
Electrical energy and power
The work done in pushing a charge round an electrical circuit is given by w.d = VIt
So that power, P = w.d /t = VI
The electrical power consumed by an electrical appliance is given by P = VI = I2R = V2/R
Example
An electrical bulb is = 100W, 240V. Calculate:
a)The current through the filament when the bulb works normally b)The resistance of the filament used in the bulb.
Solution
I = P/V = 100/240 = 0.4167A
R = P/I2 = 100/ 0.41672 = 576.04Ω or R = V2/P =2402/100 = 576Ω
This has been extremely useful when creating circuits which create heat.
On a small scale of 3cm2, this works fine. You can use thin lines in a close pattern or carbon ink, such as the carbon screenprintable ink from Ceres inks. On a larger scale, this becomes much more complicated.
Conductive thread and thin lines work well, as can be seen in the following videos:
The issues come from heating a surface and needing an incredibly high wattage, which doesn’t sit easily when working with paper. This can be found in the ‘Galaxies and Cosmologies’ project.
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