First you need to find out what size the mosaic would be if you completed it using the same number of tesserae as the original, effectively making a piece for piece copy.
The main thing to remember that in Roman mosaic work your unit of measurement is a tesserae, not inches or centimetres.
1. Find an area on the mosaic that you have a clear, straight line of either 5 or 10 tesserae.
2. Measure this line and then get your width and height of the full piece. Here it is 65 tesserae by 45 tesserae.
3. Work out the average size of the tesserae you use (I’m working in millimetres here but it’s the same for inches). My tesserae are slightly irregular, each side is 8mm — 12mm so I use an average measurement of 11mm. You
must remember that this will include something for the gaps between tesserae.
4. 11mm x 45 tesserae = 495mm, 11mm x 65 tesserae = 715mm. So if I copied this mosaic using my size of tesserae and including the same number of lines then it would be 715mm x 495mm.
This gives you the correct estimated size, don’t try to be exact. Now we move on to how to reduce it in size.
Here is an image of the original Roman mosaic of a dancing girl that I want to fit into . I use a very simple method which I’ve detailed below;
1. Find a point on the mosaic where you need a minimum number of tesserae to define the anatomy. In the case of a human figure we’re looking at the wrist and ankles (A). Notice here there have been 3 tesserae used in the width of these features.
2. Look at other areas which you can compere to the wrists and ankles which need to be seen in the correct proportion. Here I’ve chosen the neck (B). This is more of a check to ensure that however much you reduce the width of the wrists/ankles do other parts of the mosaic remain in the correct proportion. 3 tesserae width for the wrist, 5 for the neck.
3. Now look for other necessary details that you have to include in your copy to ensure it looks identifiable as a copy of this original. Here I’ve chosen the line of the body marked as shadow under her dress C.
Now the copy;
1. I’ve taken the wrists and ankles (A) down to 2 tesserae. This I regard as the minimum, 1 tesserae would just make it look too stick like.
2. To maintain proportion I’ve reduced the neck (B) to 4 tesserae.
3. You can still see the outline of her body under the dress ©.
Notice how I’ve been able to reduce the other lines of ‘filler’ tesserae but still been able to make a copy that looks like the original. At the bottom of here dress, the area stretching between the lines marking her leg, marked © consists of 15 lines of tesserae but I’ve completed it using only nine tesserae.
Originally published at http://www.romanmosaicworkshops.co.uk.