Casting methods for spandrels in the 17th century

Discussion in 'General Clock Discussions' started by novicetimekeeper, Feb 1, 2019.

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  1. novicetimekeeper

    novicetimekeeper Registered User

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    I have handled a lot of spandrels and looked at them very closely. Good ones have remarkable definition which I have assumed is part of the casting not a finishing process. I notice that they are thin, and that the high relief sections are hollowed on the back suggesting either shrinkage or pouring off the excess metal as with slip casting in ceramics.

    They have always seemed rather too fine for sand castings, but they do seem to be poured into some sort of imprint mould. They are hand finished so show little evidence of the method.

    Now, however, I have a set of modern made castings which make me wonder. They exhibit the same hollowed back, but they have the risers and vents still in place. Can anybody explain how these were made and how it might differ from the real thing?

    DSC_1020.JPG DSC_1021.JPG
     
  2. P.Hageman

    P.Hageman Registered User

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    Hi Nick, ik makes me wonder also how they were made! As you know I do cast my own brass for wheels, bridges etc. But I could not succeed in casting spandrels or thin plate. I first poored the cast into casting sand, but that did not work. Then I made a mold from plaster en heated the mold up the 250 degrees celcius and then poored in the molten brass. No succes either way. So if anyone knows how to do it, please let me know!! I enclosed a picture of the casting for the front fret of my lantern clock, a complete mess after several attempts!

    fret 1.JPG fret 2.JPG
     
  3. novicetimekeeper

    novicetimekeeper Registered User

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    I can't see how mine could be made with all those risers and vents unless both sides are in the die, so are they die cast?

    I think they must be, the chunky bits on the bottom are the risers, the three corners have the vents. If you look at the back you can see a scratched III just above and to the right of the cherub head. This would have been in the one they copied and is a mark by the clockmaker. This is probably a lost wax process, because then you could use the original to make both sides of the mould.
     
  4. Willie X

    Willie X Registered User

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    #4 Willie X, Feb 1, 2019
    Last edited: Feb 1, 2019
    You may want to try casting bronze. It has a lower melting point and high flow rates. It's made to practice jewelery making in moulds made from fine sand or plaster of Paris investment material. It has charistics similar to silver and 14K gold. The moulds have to be held at a certain temp for a certain amount of time in order for all the water to leave. Otherwise the mould can posibably explode. A taller and/or multiple sprue legs can help give you better detail without vacuum or centrifugal force.

    A sunken in back usually indicates an open mould. But, the last photo is definately cast in the usual two part mould, probably a metal one. I never did this enough to get very good at it. It's limited to fairly bulky objects. I went to centrifigul casting and then to vacuum casting and then back to centrifugal casting. I got pretty good at that. :) Willie X
     
  5. P.Hageman

    P.Hageman Registered User

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    At first I did not notice the scratched III, but that I think points indeed towards a lost wax method. I have to figure it out how ? Are there any signs of a seam on the edges?
     
  6. novicetimekeeper

    novicetimekeeper Registered User

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    I can find one short witness line that should not be there, they are very good!
     
  7. novicetimekeeper

    novicetimekeeper Registered User

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    If it is lost wax then should there be a join? Shouldn't the wax be burned out leaving a one piece mould that is destroyed to release the casting?

    Perhaps the small witness mark I can see is on the original?
     
  8. Willie X

    Willie X Registered User

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    Lost wax is very expensive of time and energy. Today, parts like this would be die cast in large numbers but if you only needed small numbers probably not.
    My 2, Willie X
     
  9. tracerjack

    tracerjack Registered User
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    The sprues look very much like what I was taught to do in bronze sculpture casting at our local junior college. Rubber was used in our class to make molds of the clay originals. Multiple wax casting were made from those. Even with our class's crude pouring method, we achieved excellent detail. I wouldn't imagine they were making large numbers of clocks in the 17th century, (correct me if I'm wrong) and labor was pretty cheap, so I would think lost wax, even if time consuming, could have been a viable method.
     
  10. novicetimekeeper

    novicetimekeeper Registered User

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    I don't think anybody would get their money back on the die for die casting these.


    This casting is modern, though I don't know when I would have said within the last 50 years.

    I think the technique originally would have been quite different, my guess is they were just poured into a shallow impression
     
  11. P.Hageman

    P.Hageman Registered User

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    Shallow impression used was my inital thought as well, but now? If they poored it into shallow impressions, I would think they ended up with a mess like the ones I got. Will start a survey on the web to see if I can find anything on this subject.
     
  12. novicetimekeeper

    novicetimekeeper Registered User

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    I can't see how it can be anything else, the backs of spendrels have no indication that they were ever in any sort of mould.
     
  13. tracerjack

    tracerjack Registered User
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    #13 tracerjack, Feb 2, 2019
    Last edited: Feb 2, 2019
    You wouldn’t need sprues and vents for a flat sand cast pour. Lost wax has datings to 3 century bc.
     
  14. novicetimekeeper

    novicetimekeeper Registered User

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    How fine can you get detail with sandcast though? I'm not entirely convinced it was a sandcast technique but I'm sure it was open pour.
     
  15. Burkhard Rasch

    Burkhard Rasch Registered User
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    I´d vote for cire perdue ;the wax positives probably were founded in large numbers in plaster forms.What makes this method expensive today is the cost of labour,cheap at the time we ´re talking about. The constituent parts of Bornholmer clocks i.e. plates and wheels and pillars were all cast and then machined.I´ve seen a rough casting of such a movement in a Denmark museum,it was flat and all parts were connected by small channels and chimneys to let the brass in and the air out while casting.
    Just an idea though...
    Burkhard
     
  16. novicetimekeeper

    novicetimekeeper Registered User

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    Lost wax for this one I agree.

    However that system involves all of the casting being in the mould whereas spandrels just have one side. Would this have been in plater though to get the definition?
     
  17. Burkhard Rasch

    Burkhard Rasch Registered User
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    "whereas spandrels just have one side." spadrels have two sides,one decorative and one not. I think the wax positives -call them father according to the process of vinyl record making- were the exact copies of the definite brass spandrel,specialy shaped on the back side to achieve equal thickness throughout the piece to avoid irregular distribution of temperature and tension and to save material.These were connected in groups and embedded in a fine fireproof material such as clay,the wax being molten out in the process of drying/hardening the clay..
    Burkhard
     
  18. Willie X

    Willie X Registered User

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    I agree with novice post #10.

    You can dust the top of the sand with finer material or simply make the whole mould with very fine sand. I've heard it called French sand or French green.

    I think the old ones were made very simply, by pounding a wood patern into the green sand and maybe dusting the mould with talc or very find dry sand. Then they would hold the mould sideways and dust it lightly, with a soft bursh, and pour away. WIllie X
     
  19. novicetimekeeper

    novicetimekeeper Registered User

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    I shall get some old ones and study the backs. If you are correct there should be some with identical backs.
     
  20. tracerjack

    tracerjack Registered User
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    I cast a large buckle in my bronze class with the lost wax method. One side with intricate detail, the other side with wax removed to lesson the weight and amount of bronze needed. That side looked just like the back of the spandrel in Post #1.
     
  21. novicetimekeeper

    novicetimekeeper Registered User

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    Well that's not surprising, I already said that was in my opinion that one is lost wax. It is a modern casting.
     
  22. tracerjack

    tracerjack Registered User
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    Yes, they could have been made this way, but then wouldn't the backs be flat or only slightly indented from the contraction of the metal. Gravity would make the molten metal self leveling. I wouldn't think you could achieve the depression that is shown on the back of the spandrel in post #1 by a flat cast.
     
  23. tracerjack

    tracerjack Registered User
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    Well, from your original posted question, I think spandrels made in the 17th century were made exactly like your modern castings. Lost wax.
     
  24. novicetimekeeper

    novicetimekeeper Registered User

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    That's a fair point. I have never understood how they were made, I assumed they pour off the excess metal as I agree it seems more than shrinkage.

    I will put together some pictures of backs for you.
     
  25. novicetimekeeper

    novicetimekeeper Registered User

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    Just a thought, one thing you do see in old castings is rag or flash, filling in the gaps in detail of the spandrels. Can that happen in lost wax? It seems more likely in a two part mould. Will get you some pics of that too.

    EDIT You see it with the so called cutouts in dial plates too. Those I think must just be poured flat.
     
  26. Willie X

    Willie X Registered User

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    Cast metal that's just poured into a mould will have a meniscus around the edge, then a slightly rounded area and then the sunken part toward the middle.
    Pouring into a cold cast iron mould will increase this effect. Heating the mould will decrease the effect.

    The processes for making intricate cast iron objects was developing then and I would guess the same techniques were used, mainly wood moulds and green sand.

    Willie X
     
  27. tracerjack

    tracerjack Registered User
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    Yes, can get bits and pieces in lost wax. If you aren't careful, the fine plaster slurry that is applied first to the wax will sometimes fail to fill in a gap or indent. And, you can get fine cracks in the plaster from the pour. I think today they use a porcelain slurry rather than plaster to try and prevent that.
     
  28. novicetimekeeper

    novicetimekeeper Registered User

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    That makes sense. Will produce more pics tomorrow in daylight, and look for risers.
     
  29. tracerjack

    tracerjack Registered User
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    Interesting topic. By whatever method they used in the 17th century, the results are impressive.
     
  30. novicetimekeeper

    novicetimekeeper Registered User

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    Spandrels are the most impressive thing they cast, and have always made me wonder, the definition on the better ones is remarkable. In technique I guess casting dialplates is pretty impressive too, I have no idea how they manage to get dialplates and movements plates so thin and consistent.

    I have always felt that sand wasn't going to give them the definition they got.

    They planished both after casting so the thickness we see was not the as cast dimension but you can see from the rag on the dialplate cutouts that they weren't much thicker. (They are called cutouts but most are definitely part of the casting process)
     
  31. novicetimekeeper

    novicetimekeeper Registered User

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    These are 17th century castings. The detail on the front is quite beautiful, there are still traces of fire gilding.

    What can we deduce from the back? What should I be looking for?

    DSC_1030.JPG DSC_1029.JPG DSC_1027.JPG DSC_1028.JPG DSC_1026.JPG
     
  32. ChrisCam

    ChrisCam Registered User
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    #32 ChrisCam, Feb 3, 2019
    Last edited: Feb 3, 2019
    Nick, certainly never cast brass but I think you will have to used fine sand, the professionals would use silicone then create a wax copy and make several using the lost wax method. You could if needed make a silicone mold to make fine adjustments first to a low melting point metal copy in stead of wax.
    Chris
     
  33. novicetimekeeper

    novicetimekeeper Registered User

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    I'm more interested in what was done in the 17th century.
     
  34. ChrisCam

    ChrisCam Registered User
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  35. novicetimekeeper

    novicetimekeeper Registered User

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    Yes, but it doesn't show anything that resembles the quality or definition we are talking about and it glosses over the early development which was already decades after the parts I'm interested in.

    I'm yet to be convinced that 17th century sand castings had the definition required. I don't know the answer, and I'd like to know, but I don't think that has moved us any further forward.
     
  36. ChrisCam

    ChrisCam Registered User
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    nick, there are in theory several alternative casting techniques, such as pumice, plaster, clay, possibly certain types of mud even but we are talking mass production and it would be the scale of that that would define the method. I think on low scale mass production there is unlikely to be a good sand alternative(and i think done by an expert you will get the required detail) but i will endeavor to come up with the definitive answer.
    Regards
    Chris
     
  37. ChrisCam

    ChrisCam Registered User
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    Nick please read: Manufacturing Technology

    Suggests until just after 1800 lost wax most likely and yes fine sand plus right ingredients can give good detail.
    regards
    Chris
     
  38. ChrisCam

    ChrisCam Registered User
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  39. novicetimekeeper

    novicetimekeeper Registered User

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  40. ChrisCam

    ChrisCam Registered User
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    Yes if your a stickler for 1769 you might be ill advised placing a bet elsewhere.
    Chris
     
  41. tracerjack

    tracerjack Registered User
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    Did a little searching on the internet for casting processes in the 17th century. In the brief history of bronze casting at thebronzesmith.com, "The most accurate and still the most popular method of casting bronze is the cire perdu or lost wax technique." I realize that's for bronze, but brass is a similar type alloy. Another site, which I can't find again indicated that for delicate or intricate castings, lost wax was preferred. Without historical documentation, I don't think we can be certain which method was used for the spandrels. Still, I think more indicators point to lost wax than sand casting. Again, those spandrels in your photos are beautiful.
     
  42. novicetimekeeper

    novicetimekeeper Registered User

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    Yes, I think lost wax seems the most likely for spandrels. They are incredibly detailed when you get early ones. Later ones were probably made using 2nd or 3rd generation moulds and have lost definition but when you see a quality early one they are remarkable.

    I assume movement plates and dial plates were different. They required scraping to get a finish and were also planished. Same for movement bars on posted frames. Pillars and posts too, originally they were cast. I don't know about wheel blanks, whether they would be sand or lost wax, and also whether the crossing out was part of the casting process. I have seen wheels that were cast with crossing out but I don't know if that was the norm.

    I have never found a foundry mark on a clock, I know Robey did a lot of research into foundry marks for the foundries in Moorfields. I must have castings from Moorfields in some of my clocks, but I've never seen a mark.
     
  43. zedric

    zedric Registered User

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    I don't think it has much information on casting techniques, but there is a fascinating history of the making of brass in the strangely titled book "Birmingham and Midland Hardware District" which was published in 1865. You can access a copy from
    The resources, products, and industrial history of Birmingham, and the midland hardware district: a series of reports, collected by the Local industries ...

    Page 232 onwards covers the history of brass making in England

    This explains why brass was expensive initially, how sheet brass was produced in batteries, and how the political environment affected the mining (smelting houses destroyed and 4000 workers either killed or forced to follow the Protector at the Kiswell mine after Cromwell came to power - after which they had to import Dutch labour). Judging by what is said, much of the 17th century copper used for brass used would have come from this mine. Brass came in several qualities, depending on the point at which it was taken in the pour (as the calamine used for zinc had significant impurities). So there was a lot to think about in terms of the quality of the raw material even before working out the technique used for the casting...
     
  44. novicetimekeeper

    novicetimekeeper Registered User

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    That's absolutely fascinating, and now I want to know more about the etymology of battery!

    EDIT> A quick google and we are there, a collection of interconnected Leyden jars looking like a group of artillery pieces.
     
  45. zedric

    zedric Registered User

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    In this case it comes from the term batter - it refers to a set of large hammers that were used to flatten the sheets. At least that's what I think... It could come from the fact that there was a group of hammers, or a battery of them.
     
  46. novicetimekeeper

    novicetimekeeper Registered User

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    Yes, the battery for brass works comes from Battre. It came to mean a collection of any metal objects and particularly artillery, and the similarity of a row of leyden jars to a row of cannon led to its use to describe a group of interconnected cells.
     

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