The Total Eclipse of the Sun Forever stamp debuted June 20, 2017. It's the U.S. Postal Service's first heat-activated stamp. Using thermochromic ink from Chromatic Technologies Inc. in Colorado Springs, the stamp's black ink spot vanishes when you press your finger on it to reveal a full moon.
Provided by the United States Postal Service

The Total Eclipse of the Sun Forever stamp debuted June 20, 2017. It’s the U.S. Postal Service’s first heat-activated stamp. Using thermochromic ink from Chromatic Technologies Inc. in Colorado Springs, the stamp’s black ink spot vanishes when you press your finger on it to reveal a full moon.

Put your finger on the black spot on the new U.S. postage stamp and the darkness vanishes to reveal an image of the full moon. Magic? No. It’s fat.

The nifty thermochromic stamp — created to honor Monday’s total eclipse of the sun and being snapped up by collectors and fun-loving folks everywhere — works like Crisco. At room temperature, the shortening is a gloppy, white paste that liquefies into a clear, shiny soup when warm. The novelty stamp, however, won’t leave fingers oily, black or cold.

“They’re esters. But it’s not like the fat right here,” said Lyle Small, pointing to his stomach, which doesn’t jiggle much at all. “These are special kinds of fat that come from vegetable sources — really specific chemicals with an exact melting point.”


Small, the founder of Chromatic Technologies Inc. in Colorado Springs, and his 54-person team provided the special thermochromic ink for the 60 million solar-eclipse stamps printed this summer by the U.S. Postal Service. It “melts” at around 84.2 degrees Fahrenheit. Also, it is the first U.S. stamp to use heat-activated ink, a technology unavailable 38 years ago — the last time a total solar eclipse was seen in the contiguous U.S. And it has helped spread enthusiasm for science across the nation.

“I’m a nerd. A proud nerd,” Small said. “And to have something like the eclipse, I will be making my way to Wyoming.”

Small plans to pitch a tent somewhere in Wyoming to catch the 160 seconds of complete blockage of the sun by the moon.

Thermochromics have been around since the 1970s. Small’s company, which he started while in college in the 1990s, has its own lab with scientists creating new molecules, perfecting colors and tweaking reactions to light and temperature. The company also is working on inks that can tell people whether their boxed milk or unrefrigerated hummus went through a high-pressure, bacteria-killing pasteurization process. And it’s working with the University of Colorado to use inks and dyes as a cancer treatment.

For now, though, Chromatic Technologies is enjoying the fun stuff.  As are philatelists, or stamp collectors.

“Well,” said John Sinski, president of the Rocky Mountain Philatelic Library in Denver, “I would say almost everybody I know that collects U.S. stamps is trying to make sure they have copies of this one.”

Some members also plan to travel to Casper or other cities in the path of the full eclipse. They’ll be taking the stamps and mailing letters back to themselves from those cities to get them postmarked on the date, he said.

U.S. stamps incorporating novel technologies are rare. In June, the Postal Service launched “Have a Ball!” stamps, featuring popular sporting balls with texture to mimic the feel of a baseball’s stitching, a golf ball’s dimples and a soccer ball’s panels.

The most memorable U.S. stamp came in July 2000 — the first U.S. holographic stamp. The space-themed stamp was the nation’s first circular one.

“We’ve seen all kinds of varieties of stamps from other countries,” said Sinski, 73, who began collecting stamps at age 8. “A lot use holograms. Some use foil. There are all kinds of gimmicky stamps, especially from smaller countries that don’t use a lot of stamps themselves but make money selling them to collectors.”

The eclipse stamp, launched June 20 and available at, is limited to a 60-million run, said USPS spokesman Mark Saunders.

Lyle Small, founder CTI , holds ...
John Leyba, The Denver Post

Lyle Small, founder CTI , holds up a sheet of stamps Aug. 9, 2017 in Colorado Springs. The US Postal Office issued a special solar eclipse stamp earlier this year, the first stamp made with heat-activated ink. Touch the black circle on the stamp with your finger to reveal the moon. The inks for the stamp was developed by CTI. (Photo by John Leyba/The Denver Post)

“The stamps have been extremely popular in large part due to the educational information it helps communicate about the upcoming eclipse,” Saunders said, “And also for its first-of-its-kind feature for a U.S. postage stamp that enables the image to change from the heat of a finger.”

The Postal Service receives 40,000 suggestions for stamp ideas a year, but only 20-25 make the cut. The eclipse stamp, which features a photo of the total eclipse viewed from Libya in 2006, has been in the works for more than a year.

Fred Espenak, a retired NASA astrophysicist who took the photo, said he was first contacted by the Postal Service a year and a half ago to check documents for eclipse accuracy. He didn’t hear that his photo, nor that heat-activated ink would be used, until around last Thanksgiving.

“I thought it was an intriguing idea. I hadn’t heard of the technology myself,” said Espenak, who is traveling to Casper for the event. “Since then, I heard they use (the ink) on beer cans.”

Chromatic Technologies does use similar ink on beer cans — specifically, the Coors Light cans that make the mountains turn blue when the can is cold. Chromatic Technologies started working on the eclipse project in April, just about two months before the stamp’s debut. Good thing the company has a library of 2,000 different inks, based on color, temperature and reaction to light.

To make UV Screen Black 29 degrees Celsius — the official name of the black ink used in the stamp — the company mixes fat, dye and developer.

The fat, similar to fats used in lipsticks and lotions, melts at 29 degrees Celsius, approximately 84.2 degrees Fahrenheit. It’s mixed with a leuco dye that can switch from color to colorless. Then the company adds a developer, which injects a proton into the dye, making the ink go black.

“The heat from your finger melts the fat, and when the fat melts, the developer disassociates from the dye and wants to become associated with the fat. And the dye shuts off,” Small said. “When I rub the stamp, I’m melting the fat. As I let go, the fat gets back to the solid state and the proton donor wants to go back to the dye.”

While the interactive stamp gives consumers an animated glimpse of what will happen Monday, pretty much everyone in this story plans to be in Casper for the event — even though bumper-to-bumper traffic is anticipated.

“This is something you don’t want to watch as a partial eclipse,” said Espenak, a.k.a. “Mr. Eclipse,” who left for Wyoming this week. “Especially if you’re in Denver, you want to get up to Wyoming. The difference between seeing a partial eclipse versus a full eclipse is like watching the Super Bowl from box seats in the stadium versus your car in the parking lot.”