The Not-Smooth Roof

The rain machine worked perfectly. That was the problem.

It made a soft silver rain over the model city. The tiny streets shone. The tiny bus stop glittered. The tiny library roof, painted with the new lotus coating, turned brown.

Maya leaned close to the plastic barrier. A muddy drop crawled down the white roof and stopped halfway, as if it had found a couch and decided to live there.

"That's wrong," she said.

Soren had already opened his notebook, not to write a report, but because his face had gone tight in the way it did when something refused to behave. "Maybe the mud is too thick."

"The regular roof is cleaner."

That was also wrong. The regular roof was supposed to show what ordinary paint did. It was supposed to stain. Instead, the raindrops on it made little trails and slipped away.

Behind them, Dr. Imani clapped once, too loudly. She wore a bright yellow jacket and had a badge that said Ask Me About Tomorrow's Materials. She was not asking anyone anything. She was looking at her watch.

"The mayor arrives in eight minutes," she said. "Please tell me the rain is not broken."

"The rain is excellent," Soren said.

"The roof is backwards," Maya said.

Dr. Imani bent over the model. "It cannot be backwards. I checked the labels this morning. The lotus roof is on the library. The ordinary paint is on the train station. The volunteers polished everything. It looked beautiful."

Maya stared at the library roof. It was very shiny. It reflected the little clouds painted on the ceiling of the display tent.

Across the aisle, real lotus leaves floated in a black tub. Their green dishes held no puddles. Water from a slow drip above them landed, became beads, trembled, and rolled away. Each bead carried specks of dust to the edge and dropped them into the water below.

The leaves did not look shiny. They looked soft. Almost powdery.

"Polished," Maya said.

Dr. Imani had already turned to wave at a group of city people in matching blue lanyards. "Do not take anything apart. There are tiny screws and I have exactly no extra tiny screws."

She hurried away.

Maya did not take anything apart. She put one finger against the plastic barrier and followed the stuck muddy drop with her eyes. It had stopped where the roof looked most like a mirror.

Soren walked to the side table. On it were extra sample squares, a spray bottle of water, a dish of garden dust, a dish of pepper, and a sign with a photograph that looked like an alien mountain range.

LOTUS EFFECT, the sign said. LOTUS LEAVES ARE NOT SMOOTH. TINY WAXY BUMPS KEEP WATER FROM SPREADING OUT. DROPS ROLL AWAY AND PICK UP DIRT.

Soren read it twice. "Not smooth," he said.

"I said that."

"You said backwards."

"Backwards can include not smooth."

He picked up a white sample square. One side gleamed. The other side was dull, like dry chalk. A small sticker on the gleaming side said LOTUS COATING, with an arrow pointing down.

Maya took the spray bottle and misted the gleaming side.

The water spread into a flat smear.

Soren did not smile. He turned the square over, dull side up. Maya sprayed again.

The water snapped into beads.

They were not like ordinary drops. They stood high and round, as if the surface were too strange to sit on. Maya blew gently. The beads raced away, gathering pepper grains as they went, leaving clean white paths behind them.

Soren put his ear close to the table. "They sound different."

Maya bent down too. The beads made tiny clicks when they hit the tray.

"Like seeds," she said.

Soren touched the dull side with the tip of one fingernail, then stopped before pressing. "If the bumps are the point, polishing would be terrible."

Maya looked at the model city. The library roof had the same shine as the wrong side of the sample. The train station roof was dull.

"They made the good side face in," she said.

"Or they used the sticker side," Soren said. "The label is on the back. The arrow points through it."

Maya laughed once. "That is a terrible arrow."

The blue-lanyard people were closer now. Dr. Imani was talking quickly, using both hands. "Self-cleaning coatings are already being tested in paints, fabrics, roof tiles, and glass treatments. Imagine buildings that need less washing. Imagine tents that shed mud after rain. Imagine a city that lets weather do some of the work."

"Except the city is currently filthy," Soren said.

Maya reached over the barrier. Her fingers found the tiny roof clips. She did not unscrew anything. She pressed one clip, then the other. The library roof lifted out with a soft pop.

"Maya," Soren said.

"No screws."

"That is not the same as permission."

"Eight minutes became less."

Together they flipped the library roof. The underside was dull white.

The model city suddenly looked less fancy. The library roof no longer reflected the ceiling clouds. It looked unfinished. Quiet. Almost like someone had forgotten to make it presentable.

A girl in a blue lanyard, older than them, stopped beside the display. "Is that the special roof? It looks dusty."

"Good," Maya said.

Soren sprinkled pepper and garden dust across the library roof. Some of it caught on the dull surface, making it look worse.

"Are you adding dirt?" the girl asked.

"For the rain to carry," Soren said.

Dr. Imani turned around at exactly the wrong time. Her mouth opened.

Maya pressed the rain button.

Silver rain fell over the model city.

On the ordinary train station, water darkened the paint and slid in slow, messy sheets. On the library roof, each drop landed and pulled itself together. The drops quivered, round and bright. Then they rolled.

They did not wash the dirt away like a river. They carried it like passengers. Pepper specks clung to the moving beads. Brown dust gathered into tiny dark crescents. The drops ran down the slope, jumped the gutter, and clicked into the collection tray.

A clean white roof appeared behind them.

Nobody spoke for a moment.

Then the girl in the blue lanyard said, "It works because it isn't smooth."

Maya looked at Soren.

Soren looked at the lotus leaves in the tub.

Another drop fell from the drip line onto a leaf. It landed on a surface covered in invisible roughness, touched only the smallest tips, and rolled off with a speck of dust riding inside its shining skin.

Maya put her palm on the table beside the sample square, not touching it. Her own fingerprints were full of ridges and tiny valleys. The lotus leaf had smaller ones. Smaller than dust. Smaller than the edge of seeing. A whole landscape hidden on something everyone called a leaf.

Dr. Imani came to the barrier slowly. Her yellow jacket had a streak of coffee near the pocket. She looked at the clean roof, then at the flipped panel in Maya's hand, then at Soren's pepper dish.

"The volunteers polished the wrong side," she said.

"They polished the pretty side," Maya said.

"The pretty side was useless," Soren said.

Dr. Imani breathed out. It was almost a laugh and almost not. "That sentence may ruin half my brochures."

The mayor arrived with wet shoes. A camera followed him. Dr. Imani looked at Maya and Soren.

"Can you do it again?" she asked.

Soren reset the tray. Maya dusted the roof. This time she used more pepper.

The mayor bent down. The camera bent down. A little boy on the other side of the barrier put both hands on his knees and lowered his face until his nose almost touched the plastic.

Maya pressed the rain button.

The roof cleaned itself again.

The little boy did not look at the mayor. He looked at the dull white panel as if it had just answered a question he had not known how to ask.

After the demonstration, Dr. Imani gave them the extra sample square. "For testing," she said. "Not for prying into any public buildings."

"What about private puddles?" Soren asked.

"Private puddles are legally complicated," Dr. Imani said, already being pulled away by three people with clipboards.

Outside the tent, real rain had begun. It ticked on the garden paths and stitched circles into the lotus pond. Mud splashed up the legs of the display tables. Water ran down the glass wall of the conservatory in long, dirty ropes.

Maya held the sample square under the edge of the roof. Soren sprinkled pepper across it with two careful fingers.

A raindrop struck the dull white surface, gathered itself into a bead, swept up the black specks, and leapt into the mud.