Soap making takes a long time, so Chi Yan plans to make lip balm first.

The raw material for lip rouge in this era was mostly cinnabar, and the main component of cinnabar is mercuric sulfide, which is highly toxic. Even after processing, some toxicity will remain, and long-term use is harmful to the body.

Of course, safflower can also be used for dyeing.

However, Chi Yan plans to use cochineal insects as raw materials. These insects mostly attach to cacti, are very small, live in groups, and are grayish-white in appearance. Because they contain red pigment, they are an excellent dye that is natural and non-toxic.

However, due to the scarcity and high price of cochineal insects nowadays, ordinary households simply cannot afford them, and shops also find the cost too high. Ba Liang had to travel to many places to buy them.

With a gentle flick of her wrist, Chi Yan added a vibrant touch of red to her fingertips.

Shen Tangning's eyes widened slightly, her gaze filled with wonder: "Is it really that amazing? Such a tiny insect can actually be used for dyeing?"

Moreover, the color is quite pure, red rather than black.

A smile played on his lips as he raised an eyebrow at her: "See? I wasn't lying to you, was I?"

She straightened up, quite intrigued: "How did you know?"

Chi Yan coughed lightly: "Reading, I guess. I don't have any other hobbies, I just like reading all sorts of books."

Shen Tangning's eyes flickered as she stared at the insects and frowned: "But how do you make lip balm from these insects? Are you just going to put it directly on your lips?"

Her heart skipped a beat, and her expression revealed a complex mix of emotions.

Chi Yan saw through her thoughts and shook his head with a laugh: "Of course not, you just wait and see."

Before making it, the cochineal insects need to be dried in the sun. Since the cochineal insects you buy are already dried, you can skip this step.

Chi Yan went to the kitchen and borrowed a stone mortar, carefully grinding the cochineal insects into powder, and then collected the powder.

Xueqing squatted in front of the stove to warm herself by the fire, then looked up and said, "Young master, the water is almost boiling."

"Okay, thank you for your hard work."

Chi Yan poured the powder into the stove and slowly simmered it, stirring constantly, until the powder was completely dissolved in the water.

Shen Tangning sat on a low stool, resting her chin on her hand, looking focused: "What are you doing now?"

Before Chi Yan could explain, her eyes suddenly lit up. "Is it to remove impurities? I remember you said it's called... purification?"

It seems that Chi Yan also took this step when making ice with saltpeter before.

Chi Yan raised an eyebrow in surprise: "Smart, and you can even apply what you've learned to other situations?"

Before she could show any demure expression, he lazily added, "But this is a little different from last time. This isn't called purification; it's called filtration."

Shen Tangning: "..."

She looked serious, as if she was thinking about the difference between the two.

Chi Yan instructed Xue Qing and Balang to each hold one end of the gauze and carefully pour the solution through the gauze into the wooden basin.

He spread the impurities on the gauze in front of Shen Tangning. She blinked, looked up in confusion, her eyes clear.

Chi Yan couldn't help but curl the corners of his mouth: "Look, do you see these things? Some of them are the corpses of cochineal insects, and some are other impurities. These things can't dissolve in water, so we have to filter them out."

Simply put, it's about separating solids and liquids.

Considering that Shen Tangning might not understand the concepts, he paused and then used a more accessible method: "For example, a cup of tea contains tea and tea leaves. To remove the tea leaves, this process is called filtration."

Shen Tangning's eyes lit up slightly: "I understand."

As for purification, it is relatively complicated, as it involves removing impurities from the mixture.

How can I explain the concept of a mixture to her?

Chi Yan suddenly realized he was at a loss for words. He racked his brains and said, "Do you remember the saltpeter I showed you last time? It was made up of individual pieces?"

Shen Tangning recalled for a moment and nodded: "I remember."

He racked his brains and patiently explained: "The saltpeter itself is mixed with other components, but these components are difficult to see with the naked eye. To remove these things, we need to purify them."