The process of enamelling slate to resemble marble was patented in 1840 by George Eugene Magnus who had spent a portion of his youth in the potteries area of Staffordshire and indeed married an earthenware manufacturer’s daughter, Mary Boyle.


As a result Magnus would have been familiar with decorating, glazing and firing pottery. In 1838 Magnus acquired an interest in a slate quarry in North Wales and another on Valentia Island, off the west coast of Ireland, with a view to obtaining slate for billiard tables.

Soon after he perfected and patented the enamelling process and set up ‘The Pimlico Slate Company’ where he produced not only billiard tables but all manner of household items. Baths, clocks, chimney pieces, wall panels and doors were just a selection of what was on offer in all types of enamelled imitation marbles and inlays.

For this article we will focus on the enamel slate chimney pieces, which were available in a myriad of styles and colours – indeed in over twenty years of restoring and reproducing the finishes I have yet to come across two the same.

The slate chimney piece or fire surround as it is now more commonly known, was an immediate sensation, being more durable, less expensive and thus more accessible to discerning architects and clients. Catalogues began to spring up from different companies which illustrations of the various designs available.

slate catalogue


The process patented by George Eugene Magnus was this:

A mixture of linseed oil, ground umber, spirit of tar and asphaltum was painted onto the slate, this was then fired in a kiln at two hundred degrees Fahrenheit for up to forty eight hours, creating a tough enamel layer on the slate. This was then hand polished into a rich lustre with pumice and rottenstone.

Different colours could be overlaid and with skilled application a variety of marbles could be replicated. A less expensive method and one I have come across most was to enamel in plain black, then dip the pieces into a water bath on which the craftsman floated a combination of oil colours. This was then hand veined and finished with a French polish.



The restoration of these chimney pieces has several stages.

For a fitted surround in fair condition it can be as simple as identifying the finish, whether it is enamel or French polish. This can be done by testing an inconspicuous area with alcohol which will dissolve French polish.

If enamelled then careful colour matching with artist’s oil colours can be used to touch up the original finish. When dry a coat of protective varnish is applied to the whole piece.

French polish can darken over time, dulling the colours of the marbling. This can be completely removed with alcohol without damaging the underlying colours and the piece can be repolished.

Unfortunately most of the surrounds that arrive at my workshop are in a sorry state of disrepair, having been painted over, left outside or broken.

The only option available in this instance is to remove all of the paint or enamel, repair and start again. Major structural repairs are carried out by the fire place company, resetting the returns on the uprights and the corbels and filling cracks and chips with a two part epoxy filler.


The pieces are then sent to me for cosmetic restoration.


The first stage is removing the old paint or enamelled finish, a process made more difficult by the banning of the active ingredient in most paint strippers, dichloromethane. Once the paint is off and the surface has been cleaned, any incised linework is cleaned out with a sharp awl. The slate is then lightly sanded.

I tend to finish them in a sprayed cellulous paint as it mimics the original enamel finish. A clear sealer is sprayed onto the slate, then two coats of black satin cellulose paint are applied.



For a grain effect, I use a tan coloured base (Dulux Heritage Gold Colour) for oak and a Burmese Ruby colour as a base for mahogany/rosewood grain. All graining is carried out in traditional oil scumbles. Grain surrounds are usually a straight brush grain, flogged to create pores. Sometimes a burl effect is employed using torn card and artist’s fan brushes.


Marble effects are done in artist’s oil colours mixed with a bit of homemade glaze (gilp) and a proprietary clear scumble. This are invariably fantasy marbles, going on a colour brief from the client.

The panels are taped off, colour glaze is applied either by brush and removed by various means or by sponge and softened with a badger softener. A flick of white spirit opens up the glaze to give a more organic appearance.



Veining is added when dry with a squirrel hair dagger brush or a feather. Any incised linework is then picked out in gold enamel paint. The finish is two to three coats of matt varnish, hand buffed with beeswax and 0000 grade wire wool to a deep lustre.


A further blog post will cover the reproduction of waterslide transfers found on most of the grained surrounds in the form of imitation inlays.


By Michael O’Regan



  1. David Agnew

    Stroke of genius indeed Mike!! Your work is awesome & huge congratulations on setting up this ‘depository’ for craftsmen & women to share their knowledge with like minded souls. All without a deceitful agenda to make gain from others knowledge which is freely shared. I salute you!

  2. Lydia Littlefield

    Michael, this is excellent. Thank you!
    I am writing my thesis (University of Massachusetts) on the subject of what we, in the states, call marbleized slate. There is very little information available, and I have been hoping to learn more about (what I thought were) Welsh and Irish techniques. Many Welsh immigrants came to the Vermont/New York slate region, bringing their slate-working skills with them. I recently returned from a trip to that area, and I will be heading to Pennsylvania to study the slate communities there in a few weeks. I believe there were slate workers from Cornwall there, as well as Wales and Ireland.
    I’m looking forward to your post about waterslide transfers. Is that coming soon?
    Thanks again, Michael. Like David, above, I salute you too!

    1. astrokeofgenius2014 Post author

      Hi Carol, either Cait Whitson or Jeremy Taylor would be more than capable of the restoration, or if they are too far from you I am sure they could point you in the right direction


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