Steamboat Springs Steamboat Springs High School science teacher Cindy Gay, who provides endless hands-on activities for her students, had yet another surprise in store for her physical science classes after blues break.
She paired up students and gave each pair a bottle of sludge.
Each bottle contained three to seven substances - solids or liquids - that had been used in freshman physical science classes earlier in the year.
The students then had a seemingly simple task: separate and identify the substances.
But for most students, the task proved anything but simple. For about two weeks and five lab periods, the teams boiled, distilled, dried, froze, filtered, picked, pulled, plucked and prodded their sludge.
The teams presented their findings to community judges Thursday.
"This one, we think, is sugar," said freshman Danielle Krey, standing in front of a three-sided display with her partner, Shealynne Yeager. "This one we think is lauric acid."
At first, Danielle and Shealynne said, they thought their bottle contained five substances. But through experiments including fractional crystallization, or the separation of soluble solids, the young women realized their bottle likely contained seven different substances.
The changing boiling points of one liquid, for example, led Shealynne to question whether it was isopropanol or methanol.
"Sludge is the ultimate performance assessment - it's authentic," Gay said of the lengthy experiment. "Did you drink a pop today? Did you use aluminum? That aluminum had to get separated from a whole big pile of rocks."
The sludge experiment taught her physical science students a great deal more than scientific procedures, experimentation and data collection.
Community judges also scored the students on elements including eye contact, posture, attire, clear pronunciation, and the avoidance of "vague terminology" such as "uh," "kind of" or "you know."
"I think they've learned a great deal," community judge Kay McGill said. "It teaches them a lot of different skills."
Danielle said dropping a heating tube and a graduated cylinder taught her not to rush, despite an eagerness to see results - and the large amount of information taught her to plan ahead.
"If you don't organize your data, it's going to be a mess," she said.
Freshman Michael Scheidel said for him, the hardest part was separating water from rubbing alcohol. He used a process called fractional distillation, or the use of different boiling points to separate liquids.
Danielle said despite the challenge of the sludge experiment, it could have been worse.
"I'm really glad we didn't get ink in our sludge," Danielle said. "I heard that was really bad."