What is the first thing I look for in getting stone for making copies of Roman mosaics? It’s supply, can I get more of it, is it easy to get hold of or would it just be a limited supply? I need to know I can get more of it otherwise I don’t use it, it’s as simple as that. The only possible exception is if I could use it in portrait work but even then I have to be sure that it is a colour that is not something I need any great quantity of. If you run out of a colour you can spend too much time trying to find more and remember, here we are talking about working to do as many mosaics as possible, to be working at a craft and not an art. The only way you get better in Roman mosaic work is by doing more, there are no advanced techniques, only experience counts.
Assessing stone samples — colour. There are two types of colour I use, a colour that is good on it’s own, it can be clearly defined as a specific colour. Also there are colours/shades that are only any use next to a, usually, darker shade of that colour. On their own they may now be defined enough to You need to have stone that has some consistency in colour. You will get variations in shade but if there is a combination of colours (think Sodalite) then you have to ask, ‘how much will I have to throw away when I cut the stone into 10mm (3/8″) tesserae?’ Also, too many veins and it will not cut well enough, it will split across the line of the vein. Test part of the stone with wax and see what the colour comes up as. Look at the stone after waxing and you need to be able to categorise it in shade and colour. If you find this difficult then the stone may not be good enough to use. Is the colour one that can be identified? By this I mean do you look at it and think, ‘It’s …..’ or is it too washed out to determine a single colour? It needs to have a specific colour or shade of colour when placed next to other tesserae. Is it red, light red, dark red? Even if it is a subtle shade that is ok but it does need to have a colour.
Above, some stones that were sent to me to give my opinion on their suitability for use in mosaic work. I am only looking at them from the point of view of Roman mosaics, i.e. large scale pieces that need a good supply. My descriptions will give you an idea of what I look for. Note; The darker shade across the middle of them is where I have applied some stone polishing wax. The effect lasted on none of them but it usually takes a few coats anyway but you need to be aware of this. Left. Hornblende, a common rock it does have the appearance of granite without the hardness. The colour is ok, not a really deep black because of the silver flecks in it but it is always good to have a cheap source of black. I don’t know the name of this stone, it is a very light brown, the black flecks in this do give it a darker shade. Can be used as a light brown Centre. Another very light brown this time with white striations (stripe or stripes of contrasting colour). As suitable as 2 above as a light brown but i would use one or the other and not both in the same mosaic. White with green striations, can be used as a very pale green but it would depend on how much of the stone has the green in otherwise you could be doing a lot of cutting for only a small amount of tesserae Far-right. Pale green, as a contrast it works fine against another green but it is too light a shade to be used on its own as green. Workability How does the stone cut? You just look at two things, is it so soft that it crumbles? You get this a lot where a stone is what is termed as ‘crystalline’ meaning it is composed of crystals. With this type of stone the fracture you make when cutting does not get transmitted through in a straight line and although be tesserae might be ok, working smaller (5mm or less) can mean too much waste. At the other end of the scale you have stone that is too hard, it can be cut but it takes a lot more time and effort and you have to ask yourself if it is worth it. This is why I do not use granite, yes it can be cut but the speckled effect you get with most granite means I do not bother using it. All of the stones that I looked at above are quite hard in terms of cutting, I would try to get these as rods either one or two tesserae wide to make the cutting easier. Going from left to right (in the above photo) here is how I assessed cutting; Hard to cut almost like granite. A fairly clean cut so this is about the best one in terms of cutting. Does tend to follow fault lines in the stone. About the easiest one to cut just watch out for where the lines are. Crystalline stone, you need to make quite a fast cut with this to ensure you get straight lines. Another crystalline stone but easier to get a straight line than with number 4.
We all have to work within a budget and getting stone cheap or free is a real bonus and allows you to get on with your mosaics but you have to balance this against the time and effort required to get it usable. Remember, mosaic work only starts when you set the first tesserae, everything up to that point is just preparation so try not to spend any more time than you need to on your tesserae prep.