Chapter 147: The Reading Glasses Lenses

For abrasives, Lin’gao had quartz sand from Changhua and local diatomaceous earth. The latter—sieved and graded diatomaceous earth—was currently being used as an abrasive for flat glass. However, Lin Hanlong decided to use garnet abrasive instead, because in this time, garnet abrasive was a common abrasive for optical lenses.

Lin Hanlong had his apprentice first sift the ground powder through a coarse sieve, then gradually switch to finer and finer sieves. Most of the industrial sieves for abrasives were brought from the old world; this time could not yet produce high-mesh industrial sieves. The final separated garnet powder became an abrasive graded by particle size.

At the same time, Lin Hanlong began to make specialized machinery for optical processing. He first used a pack of five Nanhai cigars—a limited edition from Chuqing—to ask his colleague Sun Li in the machine shop to work overtime and make a steel goblet. The technical term was a spherical grinding plate. Its inner wall was turned into a very precise spherical shape, with a pre-calculated radius. The steel goblet was a key component of the spherical grinding machine and required high processing precision, so he did not dare to entrust its manufacture to a naturalized citizen worker and specially asked a Yuanen technician to make it. At present, there were no mechanical technicians with a higher level of skill than the Yuanen.

The spherical grinding plate had to rotate on a flat surface. The technology for the transmission system was not very advanced; a mechanism like a bicycle, driven by pedals and gears, would suffice. For a more luxurious option, a power-driven overhead shaft could be used. But applying for the power to install and use an overhead shaft required advance application. Lin Hanlong was too lazy to write a report and apply, so he just went with a human-powered system—the power required wasn’t that great anyway.

The transmigrators were now very skilled at making these human-powered things. There were ready-made devices in the workshop. The spherical grinding machine also required the workpiece to be placed on a swing arm, allowing the workpiece to swing back and forth in the grinding plate while rotating. There was also a ready-made design for this. The mechanism was a bit more complex, and the power was changed from an electric motor to a hand crank. It was usable, but not very uniform in speed.

Lin Hanlong spent three weeks making and assembling the parts for the spherical grinding machine. Most of the components were hardwood, with a small amount of steel used in some places. Grinding glass by hand did not require much force, and the strength of the wooden structure was sufficient.

After finishing the processing machinery, he still needed a way to accurately fix the glass. For this, Lin Hanlong spent another three days making a series of molds and fixtures himself. With everything ready, Lin Hanlong disassembled the glass cylinder into single glass plates, wiped off the excess adhesive with alcohol cotton, and then slowly heated them on an iron plate. When the glass was hot, he took the prepared sealing wax and placed it on the glass. The sealing wax slowly melted under the heat, forming a smooth surface on top of the glass. Lin Hanlong checked it, then closed the furnace door to let the iron plate cool down. After a while, the sealing wax cooled and the shape was completely fixed. Lin Hanlong took a hemispherical mold, the top of which had already been turned into a flat surface. He slowly heated the mold, then took a piece of glass and placed the sealing wax side on top of the mold. As soon as the sealing wax melted, he quickly poured water on the mold to solidify it immediately. This fixed the workpiece to the mold.

The next step was similar to general machining. He fixed the mold to the chuck of the swing arm, then guided the swing arm into the grinding plate. The coarse abrasive, mixed with water, had already been added. He and his apprentice, one pedaling a bicycle and the other turning a hand crank, started the machine. After grinding for a while, he lifted the swing arm to inspect the workpiece, checked the grinding effect, and then put it back. After a while, the two exchanged positions. After more than an hour of this, the originally flat glass had been ground into a spherical surface. Lin Hanlong measured it with a caliper for a long time and, convinced that the precision of the spherical surface was tolerable, he removed the workpiece and announced the end of the workday.

Another day passed. Lin Hanlong applied sealing wax to the ground side of the workpiece and mounted it on a mold, but this time he used a mold with a concave top. In half a night, the other side of the glass plate was also ground.

This time, Lin Hanlong’s work attracted the interest of others. Several people stayed behind to watch the process of grinding the glass plates. The next morning, Zhong Lishi ran out of his laboratory, where he had been for several weeks, to find Lin Hanlong. He first looked at the ground rough blanks, praised them, and then asked, “After this thing is made, should the first sample be handed over to the General Office for preservation? It’s very memorable. In the future, when we have an industrial exhibition hall, this will be the number one exhibit in the optics hall.”

Lin Hanlong shook his head. “Exhibit or not doesn’t matter. I just plan to make a pair of reading glasses for someone to try.”

Zhong Lishi was a little confused. “Who has presbyopia?”

“A native. My apprentice’s father. A very good craftsman. He can’t do fine work anymore because of his presbyopia. It’s a pity.”

“Then why are you going to all this trouble? Just apply to the Planning Office for a pair. There are plenty in the warehouse,” Dr. Zhong said dismissively.

“How many can there be? The situation of presbyopia among naturalized citizens and natives is still very common, and the demand is huge.”

“Oh. These reading glasses can also be sold for money in the future.” Dr. Zhong suddenly had a business idea. Although Dr. Zhong was knowledgeable and had the air of a great scholar, he knew very little about optics.

“Someone has to try them. If they’re not made well and make people dizzy, who’s to blame?”

“Hmm. Let’s do it this way then. Can you make an extra one for me? I’ll help you make a presentation gift.”

“A presentation gift?” Lin Hanlong felt a wave of disgust. He hated this kind of formalism. He hesitated and said, “It’s not a new year or a festival. Why make a presentation gift?”

Dr. Zhong smiled. “It will be very useful.”

“Alright then.”

After the conversation, Lin Hanlong was officially assigned the task of trial-producing optical lenses, so he no longer had to do it in his spare time. This was clearly Commissioner Zhong’s way of getting him to produce the product quickly for the “presentation gift.” Lin Hanlong and his apprentice continued to work overtime, and within two days, all eight raw material plates were ground into rough blanks.

After rough grinding came fine grinding with a finer abrasive. The original abrasive paste had been cleaned up by his apprentice, and new abrasive was added. Lin Hanlong was even more careful. He had his apprentice sift each batch of abrasive repeatedly to ensure that no overly coarse particles were mixed in. After grinding for a while, he would stop, take out the workpiece, and measure it with a caliper. Sometimes he would even do it himself, using a coarse felt cloth dipped in abrasive to manually touch up the uneven areas.

In this way, it took a week to fine-grind the eight rough blanks to the limit of the caliper’s measurement. Dr. Zhong came to visit again, this time bringing Zhan Wuya. Zhan Wuya praised his product effusively. Seeing how serious he was, he advised him: they were just reading glasses. In the old world, they could be directly cast in mass production. Why be so precise? Lin Hanlong replied that it was to accumulate experience for making better optical instruments in the future. Zhan Wuya shook his head and said no more.

After fine grinding, only the polishing process remained, but Lin Hanlong was worried. The polishing powder commonly used in the optical industry was a very fine metal oxide. The only metal material Lin’gao could produce was iron. The metallurgy department said they could produce iron oxide, but they didn’t know how to make it into a powder. The machinery factory had made several ball mills for use in the cement, ceramics, and other industries, but they were all quite large. Lin Hanlong had no choice but to send the iron oxide raw material to Xiao Bailang for grinding, but the resulting iron oxide particles were not very fine. Helpless, he had to use a coarse felt cloth dipped in the limited amount of iron oxide powder to polish.

A few days later, Dr. Zhong came again. This time, he saw several smooth glass plates shining in the sun on Lin Hanlong’s workbench.

“Old Lin, you’ve done a great job!”

Lin Hanlong shook his head. “It’s a complete mess.” He took out a box from a drawer. The lid was printed with “Optical Inspection Tools.” Opening the box, Lin Hanlong put on a pair of clean cotton gloves. He then took out a piece of flannel, placed a convex lens on it, and then placed a flat glass plate on top of the convex lens.

“Look, how good are these interference rings.”

Zhong Lishi leaned closer. In the sunlight, he could faintly see the shadows of concentric rings on the flat glass. He knew this was the phenomenon of light interference, but he had no idea how to judge whether it was good or bad.

“Now look at what I made.” This time, Dr. Zhong had to try very hard to see some chaotic shadows. “The overall deformation and distortion of the interference pattern indicates that the local deviation is too large. The expected rings are practically non-existent.”

“Well, it’s the first time. It’s inevitable to lack experience,” Zhong Lishi said, picking up a piece of glass and focusing the sunlight with it.

“Look how small the light spot is. I think it’s very well made.”

“The precision still needs to be improved.”

“What kind of precision do you plan to improve it to?”

“According to the standards of the optical industry, within a quarter of a wavelength.”

Zhong Lishi almost fell headfirst onto the table. “Are you kidding me! The wavelength of light is measured in nanometers!”

“Yes. That’s the standard.”

“This is the 17th century! Can you please follow 17th-century standards? According to modern standards, what is everyone making? Scrap? Not even as good as scrap?”

Lin Hanlong remained silent.

“Can this thing be used to make a telescope? A 17th-century standard telescope, can it be made?”

“It would definitely far exceed it.”

“Then that’s fine. I think you’ve done a great job.” Zhong Lishi patted Lin Hanlong on the shoulder. “Let’s wrap these up and present them as a gift to the Yuanen Senate.”