bitumen

Also known as bitumen, asphalt is a sticky black substance derived from crude oil, widely used to construct roads, highways and airport runways.

It is more breathable but is often installed where a highly-resistant underlay like bitumen felt is already present, stopping vapour from escaping.

Volatile dilutants added to the heavy bitumen from Alberta enable it to flow through the pipeline.

The researchers discovered traces of a mixture of ochre and bitumen on several stone tools, such as scrapers, flakes, and blades.

Earlier this year when quotas were tight, traders labelled a few Iranian heavy crude shipments as bitumen mix, prompting Chinese authorities to step up tanker inspections.