Natural slate is an old, dense rock and easy to live with: in most homes a soft cloth, lukewarm water and a careful dry-off are all it needs. If you know how the stone formed and what a laser does to its surface, you care for it more sensibly and skip the household remedies that do more harm than good. This guide walks through the routine step by step, tells you where Rhineland slate comes from, and keeps workshop experience apart from what can actually be documented.
Pick up a slate plaque and you are holding a piece of sea floor. The stone we use is a clay slate. It began as mud: the finest clay particles settling out of an ancient sea, layer on layer, over millions of years. Later, mountain building folded those deposits, pressed them under directed stress and moderate heat, and lined up the clay minerals in parallel. What came out is a rock that splits along closely spaced, parallel planes into thin sheets. Geologists call this cleavage (German: Schieferung), and it is the reason slate can be worked into flat plaques at all.
The word “slate” covers a good deal of ground. Modern petrology restricts it to rocks that were tectonically deformed or weakly metamorphosed. Fine-grained sediments that were never deformed sometimes keep the name for historical reasons (the Posidonia shale or the Kupferschiefer, for instance), but they split along their original bedding, not along a later cleavage. Here we mean clay slate only, the classic roofing and writing stone.
Mineralogically it consists mainly of clay minerals, plus quartz and feldspar grains, tiny flakes of mica and chlorite, and small amounts of rutile and pyrite. Grain size is mostly well below 20 micrometres, so the exact composition can only be pinned down by X-ray diffraction. Density is around 2.8 grams per cubic centimetre, which anyone who has hung a large plaque on a wall will have noticed. Colours range from black through blackish and bluish grey to green, yellow, red and violet. The dark shades we prefer for engraving are the best known, but they are not the only ones.
In our part of Germany slate is not an import but part of the landscape. The Hunsrück slate dates to the Lower Devonian, specifically the Emsian stage. It was laid down in a trough-shaped basin, the Rheno-Hercynian Basin, a marginal sea of the former Rheic Ocean, which lay near the equator on current reconstructions. The basin kept subsiding and in places filled with more than five kilometres of sediment. Underwater turbidity currents, triggered by slumping, buried living communities quickly and preserved them. During the Variscan orogeny, when Laurussia and Gondwana collided, the beds were folded and weakly metamorphosed, and only then did cleavage develop.
The belt of Hunsrück slate is roughly 150 kilometres long. It runs through the Hunsrück on the left bank of the Rhine and the south-western Taunus on the right, north of Bingen. A separate belt lies in the southern Eifel between the Moselle and Mayen. Walk there and you walk over that old sea.
The Bundenbach slate is world famous. It counts as the most important Devonian fossil site anywhere, with more than 190 genera and over 270 animal species, among them starfish, brittle stars and sea lilies. Many fossils are pyritised: the iron mineral pyrite replaced the organism, soft parts included. Because pyrite absorbs X-rays strongly, Wilhelm Stürmer was able from the 1950s onwards to radiograph the animals inside unopened stone. In 2009 the predatory arthropod Schinderhannes bartelsi was described from here. All of this belongs to the same rock complex that supplied the roofing slate of the region.
Two honest caveats. Not every slate plaque sold anywhere comes from the Rhineland, and our own stone depends on the supplier and the batch. What we tell here describes the regional rock and its history, not automatically every single plaque.
Near Mayen in the Eifel, slate was quarried from Roman times; at the Katzenberg mine it continued until 2019. One name from that history is still a trade term: Moselschiefer, Moselle slate. It arose in the sixteenth century and refers to the old transport route, since the stone travelled down the Moselle to the Lower Rhine. In 1793 Johann Baptist Rathscheck founded the firm that carried the extraction on for generations; since 1904 the Werhahn family of Neuss has been involved. In the 1970s the Katzenberg mine and the Glückauf mine, about a kilometre away, were joined into one system. In 2003 the ninth level was opened at 303 metres depth, in 2016 the eleventh at 400 metres. At the end of March 2019 the last tub of Moselle slate left the mountain. Dressing the blocks stayed manual work to the end: diamond saws cut the blocks, but splitting them into plates of around five millimetres is still done by trained hands.
You can see all this at the Deutsches Schieferbergwerk in Mayen, a show mine beneath the Genovevaburg. In 2024 the International Union of Geological Sciences added German roofing slate to its Heritage Stones list. That is no advertisement for our plaques; it simply shows how deeply the stone is anchored in regional history. If you want to know about the people who lived in this landscape centuries ago, we have overviews on the Germanic peoples of the Rhineland and on Vikings near Aachen.
A laser engraving is not a print and not a coat of paint. In laser marking the material itself is altered, and the process and energy needed depend on the material. In deep engraving, short and intense bursts remove, depending on the material, a liquid or gaseous phase, and the desired depth is often reached in several passes. The motif therefore consists of the stone itself, changed at that spot. The technical literature on laser marking consequently describes such marks as water-resistant, smudge-proof and very durable, and as insensitive to abrasion, solvents and other environmental influences. That is a general statement about the process. For slate in particular we have no measurement series of our own; what we can say rests on workshop practice, not on a lab test.
Why does the engraving look pale on a dark ground? From what is described for laser marking (there using plastic as the example), contrast arises from light scattering on the roughened, ablated area. For slate that is the obvious explanation, but we have not measured it ourselves. What matters for care is the practical consequence: the pale area is rougher than the smooth surface around it. Dirt and grease settle there more easily, and oil soaks in more strongly. Knowing this changes how you clean and how you oil, as we explain below.
For daily care a dry or barely damp cloth is enough, ideally microfibre or cotton. Dust shows up clearly on dark, matt slate; one pass and it is gone. Fingerprints, especially on oiled plaques, disappear with a second, dry cloth. Don’t rub in circles with pressure. On the engraved area, draw the cloth in one direction so that no fibres lodge in the rough lines. For fine grooves a soft, dry brush works, such as a painter’s brush or a soft toothbrush kept for this purpose alone.
Avoid scouring powder, scouring cream, steel wool and the hard side of a kitchen sponge. Slate is softer than it looks; the surface can be scratched, and on a dark matt face every pale scratch is visible. Even the supposedly harmless “give it a good scrub” leaves fine marks that cannot be removed later.
If grease, a film of dust or kitchen haze has settled, use lukewarm water and, if needed, a small drop of mild washing-up liquid. Wring the cloth out well: the plaque should get damp, not wet. Then wipe with clear water so that no soap residue stays in the engraved lines, and dry it immediately. Drying is the step most people skip. Water likes to stand in the engraving and leaves pale rings as it evaporates, especially in hard tap water. If you live where the water carries a lot of lime, finish with a dry cloth.
How much water does the stone take? General literature on clay slate gives a very low water absorption, for roofing slate a figure below 0.4 per cent. That explains why slate survives centuries as roofing. It does not mean a plaque should stand in water. A roof slate lies at a slope, dries quickly and is exposed on both faces. Your plaque lies flat on a table, and moisture trapped underneath can leave rings or stains. So dry once too often rather than once too rarely.
Acids are out. Vinegar, lemon juice and limescale remover are not advisable on natural stone. Depending on the deposit, slate contains minor constituents such as carbonates that can react with acid, and you cannot tell from outside how much your plaque holds. The same goes for oven spray, chlorine cleaners and bleach. If a stain does not yield to water and washing-up liquid, a stronger agent rarely helps; patience and a second pass usually do. For stubborn problems send us a photo and we will see what we are dealing with.
Sooner or later many people reach for oil. A thin film deepens the colour of slate, evens out the surface, and takes away the slightly faded look the stone gets after long exposure to light. The effect resembles what a rain shower does to a gravel path: wet, it looks darker. This is purely cosmetic, not conservation in a technical sense.
Here is how we go about it. Clean the plaque and let it dry completely. Put a drop of oil on a soft, lint-free cloth, not on the stone, and apply a thin coat in one direction. After a few minutes buff with a fresh cloth until nothing comes off. Apply too much and you get a sticky film that attracts dust. Less really is more here.
On the choice of oil: commercial stone oils and colourless mineral oils are stable. Cooking oils are common and convenient, since everyone has one at home, but they can darken or smell rancid over time, especially those with a high share of polyunsaturated fatty acids. We have no study on this, only the general experience with oils on natural surfaces. If the plaque also goes on the table, choose an oil expressly intended for kitchenware or food contact.
Two honest limits. First, the stone absorbs the oil and you cannot selectively get it out again. An oiled surface stays darker even if you later stop re-oiling. Second, the rough engraved area soaks up more oil than the smooth stone around it and can turn darker, which lowers the contrast between motif and ground. If you love the bright, high-contrast engraving, oil sparingly or not at all, and test the effect first on the back or on an inconspicuous edge.
“Deyr fé, deyja frændr, deyr sjálfr it sama; en orðstírr deyr aldregi, hveim er sér góðan getr.”Hávamál, stanza 76: “Cattle die, kinsmen die, you yourself will die; but the fame of a good name never dies.” (own translation)
A slate plaque is heavy. A plaque of 20 by 20 centimetres at five millimetres thick weighs roughly half a kilogram; at ten millimetres about twice that. For larger formats plan the hanging accordingly: two hooks or a firmly screwed bracket beat a single nail, and the wall has to carry the load. For standing, plate stands, small easels or a shelf with a ledge work well. If the plaque sits loose on smooth wood or glass, small felt or silicone pads stop it from sliding and protect the surface beneath.
Outdoors the location matters. Slate is a natural stone that has shrugged off wind and rain as roofing for centuries. A small decorative plaque, however, hangs differently from a roof: water can collect behind it and freeze in winter. A covered, wind-sheltered spot, such as under an eave, is the safe choice. Permanently outdoors, algae and moss can discolour it, and the small pyrite inclusions that occur in the rock can rust under moisture and leave brownish marks. That does not affect every plaque, but it happens with natural stone. If you leave a plaque outside into winter, you carry that risk yourself; for decorative plaques we recommend a sheltered place.
Whether a plaque looks different after years behind glass or in the sun depends on the deposit, and we have no reliable figures. The engraving itself, unlike paint, is not a pigment and so cannot fade.
Slate plaques are popular as serving boards, for good reasons: the stone is dense, visually calm, and makes food look colourful. Whether a specific plaque is suitable for food contact we cannot assure in general without a specific test. We see our engraved plaques first of all as decoration, coasters and gifts. If you want to use one at table anyway, there are a few things to know. Knives leave pale cut marks on slate, and a steel knife can also leave metal abrasion that looks like a grey line. Hot pots are not a job for bare stone without a trivet: slate tolerates heat better than many materials, but it can crack under abrupt temperature change. And a rough engraved area absorbs fat and acids that you will not get out again.
Our advice: wash the plaque beforehand in warm water with a drop of washing-up liquid, dry it well, use an oil meant for food contact if you oil at all, and don’t cover the engraved motif with food. Glasses and cups on a slate coaster leave hardly any rings, but moisture should not stay trapped underneath. If you plan to use a plaque regularly for food, ask us when you order. We advise honestly, even if the answer is that an untreated, unengraved stone suits the purpose better.
Writing and engraving on slate is no invention of our workshop. Since antiquity, tablets of stone, clay, wax, ivory or slate have been used to record information, some bound together as a tablet book. From the Middle Ages until the middle of the twentieth century, slate tablets and slate pencils were produced. The Thuringian town of Steinach held a world monopoly on slate pencil stone from the late nineteenth century into the 1960s; in Engi in the canton of Glarus, tablets were made from slate of the nearby Landesplattenberg. In German primary schools children wrote on small slate tablets until the 1960s, before cheaper, unbreakable plastic replaced them. One side was ruled, the other carried squares for sums, and a damp sponge and the tablet cloth belonged to the kit.
Sharpening stones also came from slaty rock. At Eidsborg in the municipality of Tokke in Telemark, Norway, a quarry was worked for centuries to make whetstones; in winter they were hauled over the ice to Skien and loaded onto ships. The sources available to us do not say how far back this practice goes or whether Eidsborg stones were already traded in the Viking Age, and we will not guess. What is certain is that the stone was an everyday tool for centuries, not a luxury. For more on everyday Viking life see Viking trade and blacksmithing.
And runes in stone? The Norse carved their signs mainly on runestones, and these were usually granite or sandstone rather than slate. The famous Jelling stone that King Harald Bluetooth had raised in the tenth century names the king as the one who “won all of Denmark and Norway and made the Danes Christian”. We don’t need the reference to upgrade our plaques; it just shows that the wish to put something permanently into stone is thousands of years old. More in our articles on Jelling, the Gotland picture stones and runes.
Slate is not the only engraving stone, but it is one of the best for fine lines. Its very small grains allow finely resolved motifs that coarse sandstone or granite cannot take. The price is cleavage: a thin plaque breaks if dropped or if someone presses on the edge. To compare slate, wood and glass side by side, see Slate, wood or glass?. How the laser works on natural slate is covered in more detail in Laser engraving on natural slate. And if you are looking for a motif, Which rune to engrave? and Viking motifs for engraving and tattoo will help.
Honestly: it varies. The geological information, meaning formation, mineral make-up, distribution and mining history, is secure and comes from geological and regional-historical literature. The statements about the durability of laser engraving rest on general technical references on the process. The rest, such as how often to oil, which oil suits best and how long a plaque lasts outdoors, is workshop knowledge. It is well meant and proven in practice, but not backed by laboratory figures. Natural stone is also a natural product: every plaque has its own pores, veins and inclusions. What works wonderfully on one plaque may have other results on the next.
We therefore promise no effect that a stone cannot deliver. Care can improve appearance and service life; it does not replace sensible handling. A plaque you drop will break, and that is neither a care problem nor a quality problem, just physics. For gifts and fitting motifs we have separate guides: Viking gifts for men, Nordic gifts for women and Thor’s hammer as a motif; Viking symbols shows which signs are attested and which were invented.
How often should I wipe my slate plaque? For decorative plaques a dry cloth is enough whenever dust shows; plaques in kitchens or hallways as needed. Use water only when grease or fingerprints remain visible, and always dry thoroughly afterwards.
What is the best oil for slate? A colourless stone oil or mineral oil in a thin film; cooking oil works in the short term but can darken or turn rancid. Buff off the excess until nothing comes off. Test on the back or an edge first, because oil darkens the stone permanently.
Will the engraving fade? According to general technical references on laser marking it is water-resistant, smudge-proof and insensitive to abrasion. Scratches or sanding can still damage it. There is no pigment in this engraving that could bleach.
Can I put the plaque in the dishwasher? No. Heat, long soaking and aggressive cleaning tablets are unsuitable for natural stone, and the engraving may suffer. Hand washing with lukewarm water is enough.
Can I hang the plaque outdoors? Under an eave or on a covered terrace usually yes. Persistent rain and frost are riskier for a small decorative plaque than for a roof, because water can collect behind it. Bring it indoors in winter.
Why does my plaque have small inclusions or veins? They are constituents of the rock, for example tiny pyrite crystals or quartz veins. They belong to a natural product and are not a defect; no two plaques look alike.
For courage. For remembrance. For legends that live on.
Slate, Wood or Glass? · Viking gifts for men · Runes & their meaning · Thor's Hammer.
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