In order to keep the glass as a secret to the utmost extent, the vicinity of the brick kiln was heavily guarded. Everyone who worked inside was strictly monitored. Jiang Pengji had also gotten a hold of the details of their families and recent financial transactions.
Of course, all the craftsmen working in the brick kiln would receive generous remunerations as compensation every month. Their family members could also get relatively easier jobs. Moreover, children of a suitable age had priority to enroll in academies to receive education. By multiple means, the secret of the glass was well-protected. Every firing was highly confidential. Each piece of glass which was baked must be registered and defective products must be strictly destroyed.
In order to intrigue the aristocratic ladies of the North borderline, fewer pieces of glass were baked in the past. There were only more than 100 sets in total.