Alf Studios: Violin Craftsmen

Alf, Gregg T., and Que, Sharon. 
"Making Castings of Stringed Instruments." 
Journal of The Violin Society of America. 
Volume XV, No. 3, 
November 10-16 1996 at the Pinnacle Four Seasons Hotel,
 Albuquerque, New Mexico. (pp. 173-216).

This afternoon we have a talk by Gregg Alf on Making Casts of Stringed Instruments. I first met Gregg Alf in 1980 during our convention and competition year at Hofstra University in New York and to our amazement this young manówho was then only in his second year at the school at Cremona won a gold medal for his cello. After completing his studies in Cremona, he came back to the United States and with his friend, Joseph Curtin, formed the firm of Curtin & Alf of with which I am sure most of you are familiar. Since then the firm has established itself as one of the leading shops in the country. They both make instruments on their own. They make instruments which bear their joint label. I spoke the other day about these curious alliances we have between partners and theirs is one that has been very successful. Not only do they make replicas of very famous instruments, but they also make instruments on their own, according to their own designs and tastes. However, Alf is rather unique. I think, among all the makers, he has a fallback. If he were not so successful as a violin maker, he could always open a pizza parlor! And tonight, you will discover that not only he's a master maker, but he's also a master maker of pizzas.

My first encounter with plaster casting was at the Cremona Violinmaking School. It was my first day and I was waiting for a room assignment when I noticed a wall full of castings prepared, I believe, by M^o Sgarabotto. Like so many others before me, I was in Cremona searching for that magical connection back through time to the idols of our trade. Just breathing the same air was going to be wonderful, although in September Cremonese air is more like a perpetual fog. As the school year progressed, I soon realized that it was going to take more than just my proximity to the spirits of the old masters for their working techniques to rub off on me. I went back to the collection of castings, which included beautiful scrolls and ff hole reliefs from great Cremonese instruments, and recognized a direct lineage of first hand information, not just about, but directly from the great masters work. In this way, I embraced an approach to violinmaking that has served me ever since.

My first class in plaster cast making was a hilarious session held with Gil Soloman, our instructor at an evening course in restoration. Knowing how exited we were to work with castings, Gil implored us to be careful about making a mess with the fine white plaster and cited an eloquent story about the pride of some member of the Hill family in working with plaster in his fine black suit without so much as an apron, et cetera. But with 16 or so young makers, full of enthusiasm, the room was soon awash in a white cloud. Gil was a good and patient teacher and we learned from him about preparing the plaster casts and counter forms used in patch work. As a foot note, I might add that although called 'plaster', this type of casting is done not with 'plaster of Paris' but with Velmix or other plaster-like materials which are actually much harder and less prone to shrinkage.

The making of violins and the craft of restoring them have always existed as parallel yet separate disciplines. The renaissance in new violinmaking taking place today has been fueled in many ways by techniques developed in the restoration of classic instruments and by the knowledge gathered in the course of such work.

Our topic today is no exception. As you all know, castings are used in restoration, amongst other things, as a rigid counter-form for supporting patch work and for correcting archings. But the type of casting we will discuss today, although an improvement over plaster casting in many ways, is of limited use when a hard counter-form is called for. This is truly an extension of restoration techniques to the field of new violinmaking.

So, one might ask: what is the justification for making a casting of an antique instrument if that procedure is not directly applicable to its preservation? It has been our experience in replica work that the safekeeping of an instrument is in fact greatly served by producing an accurate model of its shape. It is far preferable, and easier, for example to make arching guides, ff hole patterns, and scroll templates from a urethane casting than from the original part.

Furthermore, violinmakers all seem to want dimensions for the same spots on violins and are usually loathe to accept someone elseís measurements. On a scroll, for example, one can sometimes see the accumulative effect of repeated measuring over time. But by working with a casting at hand, one can take frequent readings of any dimension throughout the scroll carving process while the original instrument rests safely downstairs in the vault.

What's more, many surface details, textures and shapes are actually easier to see on a solid white casting than on the original instrument especially when cross lighting is used. In the end, a good casting remains an invaluable reference long after the original has been returned to its owner, which is good since few artists can part with their instrument for long.

Today I would like to share a simple procedure for making highly detailed Urethane castings of violins using RTV rubber molds. This presentation has been prepared in collaboration with my colleague at Curtin & Alf, Sharon Que. It is our goal to provide you with a step by step overview of our process together with any references you may need to locate the materials and the equipment that will be described.

We have also brought some of our props which are on display at the front of the room, and we will be passing around a couple of castings and the molds used to create them. Notice that even the pores of the wood and the purfling outlines are visible. Product information sheets and even some rubber samples have been kindly donated by our suppliers and are available for you to take home at the end of the session. Finally, Sharon has prepared a set of working guidelines and a complete list of our suppliers for anyone that is interested. Please come up front at the end of the session.

At this point allow me to stress two things. First of all, I want to emphasize the responsibility we each have to protect the works of our violinmaking colleagues from the past. In pulling this material together, Sharon and I felt concerned that our desire to be complete and open with you about all our little tricks for making this work easier might backfire if it emboldened someone out there to try this with a fine antique instrument before they were qualified. Old violins are much more delicate than our own. One momentís lack of attention, a little skimping on some preparatory step, or the small oversight of some special condition that may be present can all result in damage to an instrument we love. So I am asking that, just as we are here to improve our skills as violinmakers, let us also remember to work within our ability when it comes to handling the work of others. I recommend that you not practice this on fine instruments unless you are already experienced in working with them and are trained in conventional plaster casting as well.

My work with RTV rubber molds consists basically in the introduction of a new generation of materials that carry forward the work of flexible gelatin molds. The idea was to make full castings of scrolls and to pour castings of top and back plates that could flow around and under the edge overhang so as to capture a detailed record of the edge work and an outline of the ribs. With the concept of a flexible gelatin mold I was definitely on the right track, but I wanted to contribute a few improvements to the current state of the art.

1.) To begin with, I wanted a mold that was dimensionally stable. Once cast, conventional gelatin molds seemed quickly to dehydrate causing them to shrink and shrivel beyond use unless a positive was poured at once.

2.) I also wanted a mold that was reusable. Conventional molds could only be used once as they were destroyed by the process of casting a single positive.

3.) And finally, I wanted a mold that provided fine surface details while at the same time ensuring the safety of the instrument. As with plaster, a water based mold required special care in protecting the wood and varnish from the molding material. With this separation a loss of fine detail in the positive cast was generally unavoidable. Furthermore, plaster, unlike RTV, heats up dramatically as it sets, which, particularly in combination with the moisture present, seemed like an area for improvement.

Room Temperature Vulcanizing rubber, RTV for short, provides a flexible medium that can be poured around a scroll or the edges of a top or back plate. And, it picks up even the finest details while at the same time being reusable, dimensionally stable and when used correctly, of course, is completely safe for the instrument.

But finding just the right product was quite a journey. Some rubber was so rigid that removing the model would have been impossible. Softer rubber had problems with tearing strength. One strain of RTV even releases some minute sort of alcohol vapor as it hardened which, together with its high shrinkage ratio, made it inadvisable for our use. Another more stable strain of RTV was vulnerable to chemical inhibition while hardening, caused by contact with some of the basic supplies we were using, like scotch tape and clay.

Our search did have its humorous moments, though. In one attempt at mold pouring, the medium was setting up so rapidly that we had to muster everyone in the shop for a hilarious bucket line passing small fresh batches from the mixing table, to the vacuum jar and finally on for pouring until the mold was done.

In the end, Stewart Pollens referred us to some of his colleagues at The Metropolitan Museum of Art in New York. They were an excellent source of information on the materials used in reproducing art objects for the Museum's stores and in their own restoration as well. In this manner we learned about an inert casting medium made by Dow Corning called Silastic. Before moving to our slides, I want to acknowledge, once again, Sharon Que. Sharon came to Curtin & Alf with special experience in wood model making which she learned through her work with General Motors. But more than that, she has an inventive mind which is at once disciplined and methodical and proves invaluable when developing new working procedures. Thank you, Sharon.

While the lights are still up, allow me also to pass around a few molds and castings we have made so that you can get an idea of the level of detail that can be reproduced. First we have a top casting of the ëPrince Doriaí Guarneri. Notice how the edge texture even shows the purfling outlines and how crisp the ff holes are. The casting captures the entire edge including the overhang and an outline of the rib garland. We'll show slides of this later, but here you can also see how the RTV mold was relieved so that this casting could be made without removing the fingerboard. Over here I have the mold and casting of the back plate of the ëHaddockí Guarneri del Gesu. A word of caution: these are quite heavy. When they are passed to you, expect them to weigh something like a piece of marble the same size.

In the slides we have brought, a quick overview of plaster casting will be followed by steps for pouring an RTV mold of a top plate and of a scroll. The scroll is molded in two parts with locator pins built in as an aid in reassembling the two parts when casting the Urethane positive. The top plate procedure shown is a method for molding the top and ribs of a violin without removing the top from the ribs or removing the fingerboard. We picked these two procedures as representative of more technically challenging examples of this work. We will also show a application we chanced upon for using an RTV rubber mold to remove the twist in a deformed plate which, used in conjunction with plaster positive and negative castings may prove of interest to those of you involved in restoration.

The first series of 15 slides shows my work with traditional plaster casting. Usually, this has been done in the course of restoration work when a flexible mold was not what the job called for. I include them here to illustrate the differences between the two methods of casting.

Photo 1: This is a 1716 Strad on which we're doing restoration work. As you can see I've got the back resting on a piece of plywood that has been taped down the middle. The reason for the joint is that the back is still on the violin.

Photo 2: See the head sticking out there? I am preparing for a conventional plaster casting.

Photo 4: This is the back again. Two pieces of plywood are fit close to the edges of the instrument. I then seal off the area in the gaps with clay. Like most old violins, the rib surface of the back is not in a plane. I accommodate the twist by building up some areas with clay and also fill in the rib overhang. With a hard mold, of course, if you cast an overhang you'll have a most unpleasant time removing the instrument from the plaster. I am laying down a protective layer of .001 tin foil to shield the instrument from the plaster.

Photo 5: Here I'm starting to put a dam around the instrument now that the foil is covering everything. There will be two wooden sides. Notice that in the clay I have written the name of the instrument so I can figure out what I've got later when I'm going through my collection of castings.

Photo 8: This is a close up of the same thing. Again the detailing is quite good for tin foil but the ff holes are not as defined as one gets with a flexible mold, and the edgework is missing since we donít have undercuts.

Photo 9: Here's the finished top ready for casting. I've got a paper dam around the outside. With this process, you can get a lot of details. In the foil you can see bridge impressions and some dents and wear patterns around the fingerboard, chin rest, and whatnot. With tin foil, you can get a lot of detail, but it's not as good as the RTV rubber.

To some extent it will adhere itself because it's so thin, but a small amount of fine linseed oil can be used if needed. It is imperative, however, to avoid any open cracks or areas where the open wood is exposed through the varnish. There are to many implications about this work to cover them all today but, once again, I remind us that working within our level of experience is of basic importance.

Photo 10: You can also go vertical with the foil. Here, as you can see from the interesting lower bout shape, this is probably a Bracchia that has been converted to a viola. Although the owner believes he has a Gasparo Da Salo, I think itís earlier, maybe a Linarolo. At any rate, it's a beautiful instrument.

Photo 11: Here the top ready for casting. Again, I was doing restoration work that required a hard cast. You can see the wire mesh and the wooden backing. This is standard restoration-style casting. Notice the limited impression detailing in the ff holes and edge.

Photo 12: As the last step in pouring the cast a wooden backing is installed so as to have something to clamp against without cracking the plaster.

Photo 13: For example, here I have just glued a soundpost patch in a 1734 del Gesu. Obviously this entails clamping, so a wooden backing is needed on the bottom side of the plaster counter form.

Photo 14: Lets return to the back casting to see the removal of an instrument from the cast. Here I have flipped the top over and removed the two side bars. The plaster is heating up as it sets and we are riding the fine line of waiting for a firm impression without submitting the instrument to an undo amount of moist heat. In many ways plaster casting is a little scary compared to RTV. Also you can the casting has not recorded any edge detail past the overhand.

Photo 15: Once a negative cast exists once can always pour a positive cast. Here I am making a positive for my reference from the counter form I used in the Bracchia repair. Again, you can see the limited edge and ff hole detail that results when using hard molds. This is how I worked in my copy making for many years.

Photo 16: The next series of 20 slides shows my RTV process for casting the top of a Guarneri violin. A flexible mold is made with a two-component Room Temperature Vulcanizing Rubber (RTV) called Silastic E made by Dow Corning. Then a hard positive is cast with a Urethane medium called Procast. Both products are displayed up front together with product information and the addresses of the suppliers. I also have brought the working tools we use except for our vacuum pump with which we remove air bubbles from the rubber after mixing and before casting. But I am getting ahead of myself.

Photo 17: To begin with, here's a slide showing a little cradle that we use to support the instrument during casting and a tray around it for support. Unlike with plaster casting, there is very little weight on the original instrument. These props are up front so you can see them after the lecture.

Photo 18: So you set the instrument into the cradle and then, as you saw before, just slide a thin frame up to the surface of the ribs. I usually like to cast the entire top or back plate and let the rubber flow over the edges. I do this to pick up a few millimeters of the rib profile. That way one has a very immediate reference for the rib shape which is especially useful when it comes to the shape and length of the corners. You have to hand fit a frame each time so it comes up close to the ribs, and then you use clay to fill in the gaps. You'll use clay and tape to close any areas where your rubber would escape.

Photo 19: And then you place the dam, which we reuse each time, around the instrument. This is just a mock-up.

Photo 20: Hereís the real thing. It better shows some of the important preparatory steps for casting with RTV another del Gesu. Notice how we have used a little clay to block off the area where the neck heel would be. We use the same dam for casting tops and backs.

Photo 21: Another important thing to remember is to close off the ff holes. You don't want rubber inside the violin. This is just tape. You'd think it would be impossible to adhere the tape to the inside of an ff hole and get it solidly in place, and the truth is it's not easy, but it is possible if you finish up through the endpin hole. We have a special working tool and do the final work through the endpin hole. And then, of course, you will want to put tape over the endpin hole as well.

Photo 22: Here is a close up of the special tape we use, at the top of the screen and the special clay below it. The tape is made by the 3M company. Itís called Scotch Hi Temperature Inhibitor Free masking tape. In the end, we wound up going with a type of RTV rubber that is the most permanent and dimensionally stable, but is also sensitive to chemical inhibition of its set up process. So we had to find special tape and clay that are inhibitor-free.

Well, some of the chemical components present in the glue of most masking tape and also in most modeling clay will react chemically with the RTV and it will just not set up. Such chemical inhibition from hardening is a problem with this strain of RTV rubber. So special clay and special tapes are designed which do not contain those chemicals; it's free of those chemicals and setting is therefore no problem.

It's called Clay Permoplast. That information is all in the handouts there at the front of the room. The actual clay and the tape itself is also up there for you to see. We even have some samples for you to take home if you are interested and suppliersí handouts about it as well.

Photo 23: Here is another Guarneri, the ëLady Strettoní, ready for casting. The reason I've included this slide is to show you how the edges of the dam have been lined with a yellow paper to make separating it from the RTV easier. Even though RTV will hardly stick to anything, it makes such a perfect air tight impression that a kind of vacuum effect exists in releasing it. Because it is rubber, it won't slide either. It fits so perfectly against what it is poured that you need to let air kind of get in. Where you can use it, the paper helps this. At the top of the slide, you can see how we have dammed off the fingerboard with clay. We can cast the entire top without removing the fingerboard.

Photo 24: And here we show a can of mold release spray but it is not for use on the violin.

Photo 25: So here we are, we're ready to cast. Sharon is mixing up the RTV components that are measured out by weight. We've got the table set up where we can work all the way around the instrument.

Photo 26: After you mix the rubber, the next thing you need to do is vacuum pump it out to remove all the little bubbles created while you're mixing. I realize that not everyone has a vacuum pump. They are a little costly, but they really help a lot. The RTV is placed under the bell which fits down on a rubber seal. Then you just turn on the vacuum. When we were first looking into this, there was a lot of learning curve going on about stuff like atmospheres and levels of mercury, et cetera. Our trial and error has been worth it and I am happy to pass this on to you now that we know the easy way. On the handout, I have provided information from the supplier of my vacuum pump. I also use it to pull air out of my oil varnishes and other stuff. So theyíre useful to have around.

Photo 27: This slide shows you the manufactureís label from our pump but its kind of hard to read. So if you want more information please come up afterwards for the handout.

Photo 28: So now we're starting to cast. First I am squeezing RTV like a pastry chef into the ff hole. You don't want to make air pockets, so the trick is to get it into any little areas in a smooth stream. Notice how I've also poured it around the edges here where they overhang the ribs.

For the most part nothing. The glow is just that of a beautiful fiddle. In principal RTV will not adhere to oil varnishes, but be careful. As we all know, the surfaces of violins all vary. There's often a lot of retouch. Especially on the edges and in other areas where the varnish wears thin and gets replaced with spirit-based polish and retouch, the retouch may not adhere to the wood as well as oil varnish. There's no solid rule about what you're going to encounter. So check carefully for special conditions like loose varnish and open cracks just as if you were making a normal cast. This takes some experience, so remember to work with your level of skill. Also remember that RTV will flow into any small crevices and cracks so be sure to look over your object pretty carefully. That's why I'm just imploring people to really cast their own instruments first. Experiment a little bit, don't jump right in on something. If you've done any plaster casting, you already know about keeping oil out of open cracks and whatnot.

No, none at all in this photo. But I would if there were any places where some condition called for it, such as loose retouch. Edges are especially delicate in that way.

The label says an hour and a half, but in practice the first 20 minutes are the best. Once you mix it the RTV starts setting up. The longer you go, the thicker it gets. So the best results come from doing all of the prep work well so that once the RTV is mixed all you have to do is pour. Poor results and accidents usual come from sloppy or inadequate prep work. Temperature does effect the curing rate.

Photo 29: In this slide you can see the RTV being smoothed underneath the fingerboard.

Photos 30 & 31: Finally, I pour the main part of the mold. Like with plaster, I pour along in one smooth wave so that I don't make any bubbles or trap air pockets in any of the undercut areas.

Photo 32: Here I'm just tapping around the edges to make sure that I don't have any air bubbles underneath the edge of the instrument.

Photo 33: I'm also cleaning the rubber off the dam a little bit. If you keep things tidy as you go, it makes clean up a lot easier.

To keep the RTV from flowing up into the hollowed out area under the fingerboard we've blocked it off. If you donít, an undercut situation exists that would make pulling the rubber out from under the fingerboard impossible. So we block it off underneath by taping in a flat piece of Formica which is then covered with foil so it slides out easily when we're done. We also build with clay the little dam you can see on the top of the fingerboard so that the RTV doesn't flow over this area either.

Photo 34: And here is the final result. It is the same mold thatís being passed around here.

Photo 35: On the other side, we see the area where we blocked off the fingerboard.

Photo 36: Next I have included 10 slides from another procedure. When I we were preparing to cast the back of a Strad I noticed that the top was actually twisted on the instrument as it fit to the rib garland. The instrument had recently been beautifully restored and the top had been re-barred, apparently on a flat bassbar frame. A flat bassbar frame is great for new violinmaking, but when replaced on the twisted rib garland, the Strad lost its voice. If you think about it, whatís the point of chalk fitting a bass bar if you then twist it to a completely different shape when you glue it back onto the ribs. By making a cast of the top while still glued to the instrument and then using it as a counter form while re-baring the top, the violin recovered its former sound. I might add that this is a major violin used constantly in recordings and concerts. Another reason for using the cast as a counter form while working on the instrument was that the top was a mere 1.4 to 1.6 mm thick in many places. For our own replica of the instrument we removed the twist in the plates through the procedure shown in the next series of slides.

Photo 37: First , here's the cast of the top; it is still in the RTV mold. You can see the two-part dam that's around the edges and resting below it the thin plywood scrim and below that the plywood support frame. This was the RTV that set up so quickly. The mold looks kind of weird, in part because the gauze which we added to give the rubber a bit more tearing strength.

Photo 39: This slide shows the clay, green like the RTV, which is used to fill in the spaces between the scrim and the instrument.

Photo 40: So here we have a mold of the top in its twisted shape. At this point I am at the same stage as in Slide (photo) 14. I canít tell you how much more calm this way of doing thing is and notice how this mold also includes all the edge overhand and even a few millimeters of the rib garland.

Photo 41: Next we've taken that RTV mold off the instrument and have taken the twist out of the mold by resting it from the inside on a flat wooden frame.

Photo 42: On the inside the surfaces corresponding to the purfling are now in one plane.

Photos 43, 44, & 45: Next we pour a hard base of plaster over the outside of the mold. Now we can pour our Urethane into an untwisted mold to cast a model for our replica work. That way I wonít be making arching templates and everything off a twisted plate. I've included this just to show you some creative things you can do with different applications of cast making. Anyone working with this will develop their own ideas and techniques. And, I hope you will then share some with me, too!

Photo 46: One of the benefits of Urethane as a material for pouring the final positive cast is that the shrinkage ratio is much smaller than plaster. We finally settled on a product called Procast, but there are new options all the time. Every time we do this, we do things slightly different. When I try to describe it, I fear setting a working procedure in stone. In reality, it's not that way. One is learning all the time. I'm sure I will learn new things today just from the questions and feedback about how to do something better. Here, we have put a ruler right down in the casting material to create a casting that shows us how much the RTV shrinks. The ruler has little dents in it and you just measure the scale marks in the mold over a hundred millimeters to see what the shrinkage is. We recorded a shrinkage of .2 % ( 1/5^th of 1%)

Photo 47: Hereís a shot of the Procast can itself. I wasn't able to bring it on the plane because it is rather heavy and is flammable. More information about it is on our handout.

Photo 48: The final 8 slides shows the scroll procedure. In this case we've got the pegbox filled and the scroll is setting in the special inhibitor free clay. Since these slides were made we have adopted a simpler preparation method which I will describe in a minute.

Photo 49: Notice that we haven't made the parting line on the centerline of the scroll. It's a little off to the side. The peg holes are more or less filled and some little locator indentations have been added for assembling the two halves later. We would do those deeper now.

Photo 52: Here we are removing the dam, and you have one side of the cast completed.

Photo 53: The violin is held in a little jig that allows us to flip it right over and cast the other side.

Photos 54 & 55: Next we put the dam on again and cast new rubber into that side to complete a two-part mold.

Since these slides were made we have taken to a simpler method where instead of isolating half of the scroll with clay when casting the first half of the mold, we simply fill in the peg holes and peg box and pour half of the RTV into the lower part of the frame being careful not to create any air pockets. The RTV makes it's own centerline as it is poured up. We then hang a few dowels into the rubber to create some locating pins for reassembling the two halves of the mold later on. Once the RTV sets we turn the instrument over and cast the other side, so that the mold is now two solid blocks of rubber. Remember to use mold separator between the two halves when casting the second half. RTV does tend to stick to itself.

Not really, but we have a little trick here. With your finger or a little funnel just prime any problem areas with RTV before you cast.

So that's it for the slides, if we could have the lights again I'll go back up front for questions.

Chris: I have an announcement. Gregg has agreed to teach a hands-on workshop on this subject for us at Oberlin this summer. I have some handouts which you can get on your way out. It's not just about cast making, but also about the techniques he uses in documenting and copying the fine instruments we have just seen.

Bill Atwood: I'd like to make one comment about vacuuming epoxies or other materials such as this. If you leave it in the vacuum jar too long, you'll pump out some of the volatiles that are necessary for setting and it won't harden.

Rick Miller: Have you tried cellos and are there special considerations for that?

Not yet, but if everything was prepped correctly I see no reason why one couldnít. One nice thing about RTV is that it is much lighter than plaster. When you're pouring plaster on a cello you've got a lot of weight to contend with. So there are some benefits here.

Whitney Asteroot: Did you have any problem when casting the a scroll with the Silastic adhering to itself when you pour the second part of the mold, or is that not a problem?

Yes, you do need to use a separator between the RTV and the RTV since the one thing RTV seems to stick to is itself. I showed you a slide of the Inhibitor free mold release spray. You can also use Vaseline.

Rock Eggan: When you're pouring urethane into your scroll mold, I was wondering, how do you work the bubbles out?

This can be a challenge. We have tried pre-charging the mold and also even venting. Sharon, could you please share your experience with this.

Sharon: Well, we just try and pour our urethane. Then if we notice any air bubbles we can always open up the mold and see where the problem is. After that there remains three to five minutes before the urethane sets during which time one can add a little more resin into the problem areas, re-close the mold, and then tilt it back and forth to swish the air pockets out. This usually works.

Gregg: Also keep in mind that with a reusable mold one can easily try again with a fresh cast if something goes wrong. With experience, one gets a knack for where to add a little resin before closing up the mold so as to pre-charge any areas that are prone to air pockets.

David Bell: What are the copyright issues surrounding a process such as this. Very few of us have the opportunity to examine great instruments. Suppose one started a project to market such facsimiles. What would be the copyright issues?

Gregg: I have wondered about that. It seems like historic string instruments should be in the public domain, but I really donít know from a purely legal point of view. As I recall, there has been a business recently of licensing the digital rights to certain other works of art but I truly do not how that would apply here. Just from an ethical point of view and in consideration of my clients I try to remember that an artist might be sensitive about having a million copies of his violin or her violin floating around. Such an approach of human sensitivity has usually served me better than a strictly legal route anyway.

In terms of time, I want to be fair to Amnon who's coming up next but we have time for a couple more questions.

My name is Dick Cook. I'm curious. You're talking about casting urethane but also that Silastic E is a RTV rubber, not urethane. I'm kind of puzzled as to when you use the RTV and when you use the urethane.

Gregg: Wow! I have a humorous footnote about that in the handout. Just to remember that a flexible RTV rubber mold is made around the instrument first and then the hard Urethane stuff is cast into the RTV mold. If you do it the other way around, youíll be in big trouble.

Joseph Grubaugh. Have you ever thought about using wax down first to protect the varnish, etc. I mean would that be . . . I forgot the word you used . . inhibitor free.

You know, I have been wondering about that too. I hope next year when we're together there will be a lot of new experience from people who have experimented with this. I don't think that the wax would be an inhibiting compound . . I'm not sure . . . but I am interested in wax and in the debate with regards to its use on fine instruments. Joe, I would really appreciate any information you might also have about the use of wax in finishing new instruments as well.

Sharon: The obvious thing is just to test it out. We are always testing everything. Tests on shelf life, tests for inhibitors, all this stuff. So I would say, just do a little test. The other thing is that Dow Corning is excellent to work with because they have a really good technical assistance program. You can call and talk to them and they're really helpful. But test stuff first . . . not on the real thing.

Gregg: Yes. Test a hundred times. Most of our work is in testing and researching ahead of time. Then there is lots of preparation work. When you have done this well the final casting goes fairly smoothly.

Well, my friends, our time is up. Thank you very much for allowing me to share this with you today.

Fill in peg box. First line with plastic then with clay. Fill in peg holes half way.

Cut out counter form - back all surfaces that come into contact with RTV with paper attached with rubber cement. Mark how far to fill with RTV. Fill holes with clay.

Mix RTV. With finger, fill peg holes. Put RTV in funnel and squeeze into place. RTV is like taffy so it can be hard to manipulate; it does have very good settling properties. Work quickly as it thickens rapidly. Fill to parting line.

Check over violin for cracks, loose varnish or any potential problem areas where RTV might cause problems.

Mask off ff-holes using non-inhibiting tape from inside using special tool to work from inside through endpin hole.

Fingerboard - spot glue a series of shims to under surface of fingerboard. This is to avoid undercuts. Then cover with tin foil acting as a separator.

Place violin in cradle. Place collar around ribs. Adjust height. Cover with tin foil - this is the separator. Fill gaps between collar and ribs with clay. (Collar is made from thin plywood; it is built up to about 5 mm below top plate. Screwed together at center line of instrument. Fits closely to the ribs.)

Cover dam with paper attached with rubber cement. Place dam on collar. Clamp down. Fill holes with clay.

Pour RTV. With a funnel squeeze a thin stream of RTV under fingerboard, into masked off ff holes around edges.

Use separator, where necessary. RTV does not stick to most surfaces but being rubber neither does it slide. Paper or tin foil is useful as a separator where RTV comes into contact with dams and counter surfaces.

When separating the mold from the violin parts, a kind of suction cup effect or air lock caused by the precise air-free fit of the rubber impression is over come by peeling the mold back in a way that allows air to enter.

Firmly secure instrument while doing set-up work. Most of your time and effort will be in getting ready to pour RTV.

Test RTV before use. It does have a short shelf life. Also test for possible inhibitors.

Have everything ready to go once you mix up RTV. Plan on working quickly. Effective working time changes with shelf life and working conditions always seems to be best during the first few minutes after the RTV is mixed.

It is strongly advised the you use a vacuum pump and bell jar to pull air bubbles from the rubber after mixing.

Petroleum jelly works good as a separator between RTV and RTV, a two piece mold.

Can use the heat from a light bulb to speed up cure. Be careful not to overheat the varnish.

Once the RTV mold is made, pouring a positive cast is as simple as mixing the two components together.

Use a small funnel and probe to work resin into any areas where air pocket might form.

Remember, RTV goes on the instrument and Urethane goes into the RTV mold those results. We do not want any emergency calls from friends that reverse this process!!

Different Urethane products have varying shrinkage ratios and better products are available all the time. We currently use ProCast 20 which is available in three colors. But, keep experimenting!