the most common humidors used a clay brick which absorbed water and released it inside of a box: they were usually soaked and released bubbles until they were full. I believe it was called 'aztec' clay - the concept was similar to today's oasis foam. Back then humidors were commonly lined with tin or 'milk glass' - this is a white glass you will find in antique humidors. If im not mistaken, the credo brand, reverse osmosis humidification units did not come out untill the eighties...