Artificial Stones
Den Haag

Many stones that wash up on the beaches of The Hague's North Sea coast are not of natural origin. Instead, they are waste products of various industrial processes that have found their way into the environment. Between shells, sand and driftwood, they reveal the blurred line between natural and artificial materials.

Beach ExhibitionsResearchRestoration Work

Metallurgic Slag

Slag is a waste product of pyrometallurgical processing of various ores (1).
Although this material has always been used in various ways, slag was considered waste for a long time. But among other applications, steel slag was used as ballast for ships in the 1600s (2) and dumped near harbours. This and the deliberate dumping may have led to this material being found so often on the beaches of The Hague (E-mail conversation with Dr Michael B. Parsons).
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In general, any type of slag contains chemicals of environmental concern. Slag containing ferrous metals may have a higher potential for negative impacts, because they cause alkaline leachate due to the dissolution of copper oxides and silicates (3). Today, slag is used for various applications: Construction of roads, concrete for bridges and walls, agricultural uses or for insulation (4).
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In the Bronze Age, many new and different metallurgical processes were developed in the Mediterranean region. The resulting glassy slag was possibly used for jewellery and glass, as a high proportion of these by-products have been found in beads dating from this period (5).
It seems that slag is everywhere and that it causes a little disappointment to many people who think they have made a geological discovery. Is it slag? It's slag ಠ_ಠ (6)

Clinker

Clinker is a dense residue left behind when coal is burnt. The objects made of this material found on the beaches of The Hague most likely came from ships that used to run on coal. From the 1800s to the mid 1900s, clinker from the ships' ovens was dumped directly into the sea. From the remains of this material on the seabed, old ship routes can still be reconstructed today. (7)
An other source for these objects could be household coal stoves, as in the Netherlands, before electricity, heating and cooking was mostly done with coal.

On sandy and muddy seabeds, clinker can serve as an attachment for various creatures and plants, such as sea anemones, and thus increase biodiversity. On the other hand, clinker seems to be toxic for other species and is covered by sand after some time. (8)