@Nunally it's the same process, making the magnifying glass first won't help.
They're trying to make the glass blank first, without knowing the full manufacturing method.
Edit: for those wondering, this website has a pretty good breakdown of the entire optics manufacturing process http://www.madehow.com/Volume-2/Telescope.html
Shizuko and her glassblowers probably don't have access to good quality materials (quartz) and high enough temperatures, around 1550C.
@moozooh
Dr Stone is hardly what I'd call realistic in terms of manufacturing. Specially so since so many of the people involved are super duper human geniuses at their respective crafts.
Matsunaga? Isn't he depicted as the castle builder old guy in Nobunaga's Chef? This one is too young. If i want to take a guess, he's Saru from the depicted sideburn he sports.
Actually, have we ever seen Nobunaga's retainer except Mori Yoshinari?
omg when I was thinking "Agriculture turned to engineering/material genius, borderline impossible" then they clarified craftsmen making ideas like that come true with their knowledge instead of Shizuko knowing every detail, making it believable.
@Grimmycoffee Yes That's definitely might be Matsunaga Hisahide and just like in historically and how he depict in every media he always be portrait as cunning and ambitious tyrant, he heard the rumor of the Oda clan resource, wealth and Shizuko. if you look at his dialogue looks like he was trying to achieved everything or forcing shizuko to use her wits had for his own personal ambition like how Konoe want to adopt her because of her genius thinking.
Oh yeah, Since Ashimitsu was Ashikaga Yoshiteru, i wonder what is the role of Ashikaga Yoshiaki ( Yoshiteru's brother ) is nobunaga will be make Yoshiaki a puppet shogun or Ashimitsu control behind the scene by disguise as another person ? we finally see many daimyo and I think Oda and Shizuko will have a big problem like
Azai Nagamasa betrayal, Yoshiaki make coalition against Nobunaga, Nobunaga will Massacre everyone including Monks,women and Children, Takeda's & Uesugi invasion, Many of Nobunaga's retainer and Matsunaga will betray him.