Filing peaked at 12 families in 2022 and has flattened since, based on 47 tracked families from 2015 onward. That pattern suggests the core thermal and chemical tempering processes are largely claimed, though a smaller cluster of control-systems and machine-vision filings around cooling automation and defect detection is still showing activity. Anyone assessing freedom to operate should focus due diligence on that newer control layer rather than the core furnace and ion-exchange chemistry, which is older and more heavily cited.

Physical (thermal) tempering uses rapid air cooling to set surface compression, and chemical tempering uses ion exchange in a molten salt bath, typically for thinner substrates. Both appear among the most-cited records in this dataset, with one top-cited filing covering thin-glass physical tempering and another covering the ion-exchange process and molten-salt chemistry for thin-glass chemical tempering. The persistence of citations to both routes indicates neither has displaced the other; the choice tends to depend on glass thickness and end application rather than one process being clearly superior.

Ownership in this dataset is fragmented: 47 families are spread across a long list of assignees rather than concentrated in two or three dominant players, and only two co-assignee pairs appear across the whole set. In the most recent tracked year, only one assignee shows any filing activity, with the rest — including several Chinese glass processors and a Korean holding company — showing none. That combination points to a field where IP is held individually and defended piecemeal rather than pooled through joint filing.

The under-claimed areas sit outside the core C03B glass-forming claims, in the smaller IPC clusters: in-line fragmentation-pattern imaging, anisotropy detection via machine vision, AI-assisted cooling-zone control, and heat-soak defect prediction. These subclasses (G05B, G06N, G06T, G06V, G01N) appear in single digits against 47 core filings, meaning the process chemistry is crowded but the monitoring and control layer around it is not. A first claim there would likely combine a sensing step — imaging or spectral — with a closed-loop adjustment to furnace or cooling parameters, rather than claiming the glass process itself.

US6279350B1, assigned to Uniglass Engineering Oy and granted in 2001, claims a method and equipment for adjusting cooling air in a glass tempering machine, using fans and a closing device to raise pressure in a reduced tempering zone so that thin glass tempers evenly without a separate zone. It is one of the more heavily cited records in this dataset. Its age means the core claim is likely to have run its full patent term in most jurisdictions, but its citation weight signals that later cooling-zone and pressure-control filings should be checked against its specific claim language before assuming clear space.