Coke oven plant Zollverein, Essen, Germany. Cross-section through a multi-layer wall for heat storage and heat-insulating the interior of the coking plant. Leftmost a concrete wall as the end of the battery, then a brick wall, then two fireclay walls, on the far right is the first heating wall formed from silicate rocks.
<a href="//commons.wikimedia.org/wiki/User:Smial" title="User:Smial">smial</a>
<span class="int-own-work" lang="en">Own work</span>