At Aztalan, besides pottery and stone tools, people crafted items from animal bone, shell, and copper. Shell was fashioned into spoons, pendants, and beads, and native copper was used to make fishhooks, beads, and earspool coverings. Hollow and lightweight bird bones were made into flutes and used for ornamentation, while harder deer bone was worked into awls, bone needles, and other tools. Fibers from tree bark and other plants were used to make clothing, bags, netting, and other items. Plant materials were also mixed as a binder with clay and used like plaster to coat the outside of houses and stockade walls. When the structures burned, the fire baked the plaster into a hard, brick-like material. Visitors to the site in the mid-1800s misidentified the baked plaster as mud bricks, and today archaeologists know this material as "Aztalan brick".