Crystals
There's a fantasy trope in which the keepers of an eldritch entity become changed in some way by it (such as dragon-riders becoming dragon-like and growing scales and pointy ears). What if something like that happens to Titan engineers? The Titans' core energy gradually crystallises and forms a layer on the inside of the core chamber, which has to be periodically scraped out so it doesn't affect core efficiency. Despite every precaution the engineers take, the crystallised dust and tiny shards get everywhere, including accumulating in the engineers' casings. The Titan engineers eventually become characterised by their warped-looking but strangely beautiful crystal growths that can't be removed from their frames without damage.
Material like fordite builds up in Titan hangars and is sought-after for making keepsakes and jewellery.