The greening of Chicago's restaurant scene hasn't happened overnight -- it's been more like a slow-growing (but far friendlier) Audrey II -- but restaurants and diners now have something concrete to look to that makes it official.

The Green Chicago Restaurant Co-Op on Tuesday will announce 15 restaurants that have earned "Guaranteed Green" status and the corresponding label they can, and most certainly will, display in their businesses, Zagat sticker-style.

The restaurants are: Avec, Big Jones, Blackbird, Bleeding Heart Bakery, Blind Faith Café in Evanston, the Dining Room at Kendall College, Frontera Grill and Topolobampo, Keefer's, Poag Mahone's, Roti Mediterranean Grill, Simone's Bar, Sopraffina Marketcaffe, Trattoria No. 10 and Uncommon Ground.

The Chicago Diner, Hamburger Mary's and Jacky's on Prairie are currently pursuing certification, says Andrew Weithe, the co-op's assistant director of environmental affairs.

The co-op, founded by Trattoria No. 10's Dan Rosenthal and Ina Pinkney of Ina's, launched the Guaranteed Green program last August.

The little label signifies a great deal of effort. It means the restaurants have earned certification (some as recently as last week) from Green Seal or the Green Restaurant Association, two independent, national organizations; thus far, all the certification has gone through the latter group.

This process can take months and cost thousands of dollars, and it doesn't just mean the napkins and plates are recyclable. Nor does it mean restaurants can coast after year one; certification must be renewed annually.

Diners also will soon be able to spot the labels for green-designated eateries in the dining guides of several publications, including Chicago magazine. The city's tourism website will post the list this week; the environment department and Chicago Climate Action Plan link to it as well.