Making a scroll cast using foam

An efficient method of casting a scroll that eliminates the need for silicone rubber

Makers reveal their special techniques

Luthier based in Flesherton, Ontario, Canada

The following method for making scroll templates is something that I developed for workshop use when making bench copies, if there are time constraints when it comes to access to the original instrument.

The practice of copying violins has been around for centuries, and that process generally begins by making drawings and taking measurements of the original. While tracing the outline of the front and back are fairly straightforward, the scroll presents more difficult challenges because of the dimensionality of the shape, and it cannot simply be traced.

This method has many advantages compared with alternatives such as making silicone negatives or working from photographs. Silicone casts require quite a bit of time, as well as the removal of strings, and photos present the challenges of getting accurate and squared images because of all the angles and cants within a scroll. They can often also be quite distorted. This method of creating casts for templates is quite simple and practical, and has the advantage of being able to get accurate representation from the maximus line, which later allows for any under- or overcutting in the final sculpture. It is also safe for the varnish and will not remove any patina within the scroll, as silicone sometimes can.

Here, I am making a template of a 1767 Guadagnini violin. As with working with any instrument, the greatest of care and understanding of materials must be fully observed and practised at all times.

Bass side scroll of 1767 Guadagnini

1 First, I thoroughly examine the scroll for any open cracks or damage. Nothing will be cast until any required repair work is completed. I ensure that the pegs are turned so they fall within the pegbox outline.

A negative is made

SCHNURR PHOTO DAVID VAN ZANDT. ALL OTHER PHOTOS MARK AND PATRICIA SCHNURR

2 I use orthopaedic impression foam to make a negative. It is a very low-density foam that impresses easily and with minimum force. I press the scroll into the foam squarely, using the centre spine as my reference. I stop the impression just past the centre. I ensure that the spine is fully submerged in the foam, as it is sometimes proud of the outside profile, and this will give the maximus line for my template. Sometimes there will be a little foam that comes off in the pegbox, which can easily be removed with a soft-haired brush, or by blowing on it.

Mixing the plaster

3 I then mix the plaster according to the manufacturer’s guidelines. Here I am using Ultracal 30. I like this plaster because of its low maximum expansion rate of 0.08 per cent.

The plaster is poured in

Smoothing the plaster with a trowel

4 I pour the plaster at a slow, even rate up to the surface of the foam (4a). I don’t have a vibration table, so I just jiggle t he box to level the plaster and help release any trapped air bubbles. I then top up the negative, trowel off the surface (4b) and jiggle a little more to level the plaster again. I then set it aside and let it cure before removing it from the mould.

Removing the foam

5 I remove the casts by c arefully breaking away the foam.

Cleaning the casts

Cutting off the pegs

6 I clean the foam off the casts with a stiff brush (6a). An air compressor with a blow gun also works well. Then I cut off the pegs with a saw (6b).

Filing down the plaster

7 I use a file or sandpaper to remove any p laster that has overflowed and created a burr, and reclaim the fluidity of line.

Making an outline on paper

The outline is finished

8 Now I can trace the outline of the scroll from the cast, knowing that the inside of the line is the outline of the scroll, and is the line I’ll want to cut to when carving the scroll.

Drawing the turns

9 I like to draw the turns freehand, as I feel it helps with k nowing and understanding the motion and intent of the original. I believe this translates well in the carving process, as the lines and their movement have been thoughtfully examined and conceived. You now have an accurate drawing that can be used as a template in the traditional manner.