Unknown Maker, Roman

The flakiness and iridescence of this bottle are evidence of deterioration due to weathering. The weathered layers of the glass are part of the object; they are not dirt or minerals that have fused to the glass. Seasonal wetting of the soil leached alkali from the exterior of the object, leaving a layer of almost pure silica behind. As the glass weathers from the outside in, subsequent wet seasons will leave a buildup of silica layers. There can be dozens of these layers, even hundreds. The brittle silica layers create a flaky effect which refracts light, giving an iridescent appearance.