Abstract: Glass articles including a glass laminate substrate having a plurality of flow channels formed therein are provided. The glass laminate substrate includes a first glass layer and a second glass layer fused together. In various embodiments, at least 80% of a total area of a floor of each of the flow channels has a local surface flatness of less than 100 nm/mm2, measured along a length and width of the floor of each of the plurality of flow channels Such glass articles are manufactured using a method including contacting a first portion of the first glass layer with a first etchant for a first etch time to at least partially form flow channels in the glass substrate and contacting the flow channels with a second etchant for a second etch time to flatten a floor of each of the flow channels.