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    « How to make a scroll cast (part 2) | Main | Note to the varnish makers »
    Thursday
    Aug252011

    How to make a scroll cast (part 1)

    I am often asked how to make a scroll cast.  I find casts useful when I am carving a scroll or shaping the arching of a plate.  I have detailed with photos the steps on how to prep a scroll and cast a two part silicon mold that can be opened and closed several times.  This is important because being able to completely open the cast will prevent damage to it as you remove the positive which may stick in some areas.

    I have a list of what materials to use and how.  Credit goes to Sharon Que who is the go to person for cast questions and informations.  She is a talented restorer in the Ann Arbor area and an expert in casting vintage violins.

    Violin maker Gregg Alf also presented this method at the 1996 VSA meeting.  After the photos is the transcription of his lecture, it is long and detailed, which gives you an insight about how thoughful Gregg is, if you are planning to cast a scroll certainly worth reading.

    The peg box has to be filled, leaving just 3-4 mm of pegbox wall.

    A small spatula and even a brush can be used to smooth the surface.

     

    The box can be taken apart and put together with screws.  It is made of playwood.

    Notice the indentation to allow the neck to go through the box.

    The peg holes and a small fracture were also filled.

    Thank you Albert.  (Albert Mell presenter)
         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 Mo 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.
         Secondly I would like to thank all those who have shared with me their own experiences about cast making. It is upon their generosity that this work is built. Luiz Bellini was very gracious in introducing me to the use of a flexible mold for makings full castings of scrolls or other parts where undercutting is present. This method involved the preparation of a water based gelatinous medium that could be poured around a part with compound curves, removed once it set up, and then reassembled as a mold for pouring a plaster positive. That afternoon with Luiz, I also learned something special from the satisfaction he seemed to experience in the open hearted sharing with a colleague. And so, I am also most grateful to him for the opportunity to share this with you today.
         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.

    Thank you Albert.
         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 Mo 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.
         Secondly I would like to thank all those who have shared with me their own experiences about cast making. It is upon their generosity that this work is built. Luiz Bellini was very gracious in introducing me to the use of a flexible mold for makings full castings of scrolls or other parts where undercutting is present. This method involved the preparation of a water based gelatinous medium that could be poured around a part with compound curves, removed once it set up, and then reassembled as a mold for pouring a plaster positive. That afternoon with Luiz, I also learned something special from the satisfaction he seemed to experience in the open hearted sharing with a colleague. And so, I am also most grateful to him for the opportunity to share this with you today.     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 Prince Doria 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 Haddockí 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.

     

    To be continued.

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