The main ingredient for mosquito coils was chrysanthemum used as an insect repellent.
This plant originally came from Yugoslavia in the Earth era, but in Zheng Qian's current Hua Xia, it did not exist.
So, to make mosquito coils, she needed a substitute: ancient Hua Xia realgar, which could also repel insects.
Zheng Qian used her personal brain terminal to look up the formulas and methods for making mosquito coils.
"Powdered mugwort, pine resin powder, tobacco leaf powder, sawdust powder, a small amount of sulfur powder, and an extremely small amount of arsenic powder—rolled into a spiral-shaped coil, it can burn for three to four hours."
Sulfur and arsenic were both toxic, but discussing toxicity without considering the dose was nonsense.
Once burned, the release of these substances in the room was minimal—almost negligible—and would not cause illness.
Even in the space era, mosquito coils contained substances harmful to humans.
The next morning, Zheng Qian got up and wrote down the list of ingredients and method, asking her maid Xiuzhu to go purchase them.
Xiuzhu was the most trustworthy; Zheng Qian had full confidence in her.
"Miss, the arsenic…" Xiuzhu hesitated. "Why do we need arsenic? If anyone in the household found out, who knows what gossip they'd start?"
"Shh, that's why I'm sending you, not Cai Yuan or Red Luan," Zheng Qian said, winking. "Go quickly and come back quickly."
Xiuzhu: "…"
Steeling herself, Xiuzhu set out. Since her mistress trusted her, she would get the job done properly. Even if she were asked to drink arsenic herself, she would obey.
After Xiuzhu left, Zheng Qian asked Cai Yuan to fetch a clean large pot, and Red Luan to get bamboo mats used for drying grain.
The maids went about their tasks.
By afternoon, drenched in sweat, the maids had gathered all the items Zheng Qian needed.
She had Cai Yuan place the pot in a separate wing of the house, set up a small furnace nearby, and forbid anyone from approaching, only letting Cai Yuan stay to assist.
She also had Cai Yuan bring her small locked chest.
Zheng Qian could have directly taken things from her spatial storage, but to avoid frightening Cai Yuan, she first reached into the small chest and pulled out two sets of protective suits, masks, and goggles.
Cai Yuan was stunned.
"Here, help me put these on," Zheng Qian instructed.
She taught Cai Yuan how to wear them. Cai Yuan quickly learned, helping Zheng Qian dress, and Zheng Qian helped her adjust everything properly.
"First, we need to sort through the spices, removing all impurities," Zheng Qian explained.
She guided Cai Yuan through the process; Cai Yuan followed swiftly.
While sorting, both wore masks, making it hard for Cai Yuan to breathe. After a while, she adapted and hoarsely asked, "Miss, what exactly are we making?"
"Incense," Zheng Qian replied.
"Incense? You know how to make it?" Cai Yuan asked.
"Not really, I just learned temporarily," Zheng Qian smiled.
"Learned from where?"
"I have a master in my mind," Zheng Qian said.
Cai Yuan trembled uncontrollably, stiff in the back, unable to hold the spices properly.
When the young mistress healed Fifth Young Master's illness using items seemingly out of nowhere, Cai Yuan hadn't dared tell anyone. Rumors had spread that the mistress was a disciple of the ghost doctor Lu Qi.
Now Zheng Qian mentioned a master in her mind—was it that same ghost doctor influencing her?
Zheng Qian seemed to sense Cai Yuan's thoughts. Through the goggles, she smiled: "Don't be afraid. I'm not possessed. I'm still your mistress. My master in my mind only helps us; it won't harm anyone. If you treat me well, it will help you too."
Cai Yuan, considering the sudden change in circumstances and seeing her mistress's abilities, was already about 70–80% convinced.
"Miss, how do you make things appear from nothing?"
"Shh, don't ask. My master says some secrets shouldn't be revealed," Zheng Qian said, smiling. "Ask too much, and my abilities could be taken back, and I'd have to suffer under the family again."
Cai Yuan immediately fell silent, her heart warmed. She felt like crying.
With her mistress's adventures, no one would dare harm her again.
Cai Yuan's hands were steady now as they carefully sorted the spices.
After removing all impurities, Zheng Qian roasted the spices.
Once roasted, the two removed their protective suits, opened windows for ventilation, and left the wing.
Zheng Qian still forbade any maid from approaching, letting each busy themselves, only keeping Cai Yuan nearby.
"Grind all these into powder," Zheng Qian instructed.
The summer heat and the suits they had just worn left both soaked in sweat, as if immersed in water. Grinding the spices only added to their perspiration.
Once finely ground, Zheng Qian had a small stone mill brought from the kitchen.
She mixed the ground spices with water and used the stone mill to turn it all into a paste.
By this time, evening was approaching.
Zheng Qian placed the paste into a wooden barrel to settle overnight.
The next morning, with the paste settled, Zheng Qian began making the incense.
Cai Yuan still assisted, while the others busied themselves elsewhere, forbidden to disturb the work.
"We'll divide the paste into two batches. The first batch mixes with sawdust powder to make the incense core, which will be firm; the second batch is diluted with water, then mixed with sulfur and the further-diluted arsenic solution," Zheng Qian explained.
Cai Yuan nodded.
Making the incense core—especially the spiral shape of mosquito coils—was extremely difficult.
Zheng Qian failed twice before finally completing one coil.
She placed it in the furnace to dry it slowly.
She made ten incense cores, and by the third morning, they were fully dried and shaped.
The added sawdust made them sturdy yet combustible, based on data from her brain terminal.
"Not easy," Zheng Qian smiled.
Cai Yuan agreed.
Next, the incense cores were dipped in the second batch of paste, which contained realgar and arsenic. Extreme care was needed.
Each batch required four rounds of dipping and drying.
After five days, Zheng Qian finally produced ten mosquito coils.
"They're not perfect; I can't perfectly align two spiral layers," she thought. "No matter, when I sell them to Prince Ancheng, his workshop's master artisans can perfect them."
That evening, she brought the maids to a small pavilion in the back garden for dinner.
The pavilion was near the water, low-lying, and usually infested with mosquitoes. Zheng Qian wanted to test her mosquito coils.
She set the meal on the stone table, a small table beside it for the maids, everything ready.
Just as they were about to eat, a voice suddenly asked, "Why are you dining in the back garden?"
Everyone was startled by the sudden interruption.