Casting with yellow brass

I am restoring a clock dating from around 1710 which is missing about a third of its original parts, some of which need to be cast.

Clock cognoscenti are very particular about the colour of the brass used in restoration. Early clocks are invariably made of soft yellow brass which, for moving parts such as the wheels, needs work hardening.

I made patterns for the castings and sent them off to a foundry to be cast using the lost wax process. After receiving them the foundry called me to say that they couldn't use yellow clock brass with lost wax because of problems with the fumes, but they would use an alternative and I wouldn't see any difference.

When I received the castings they looked very yellow on the surface, but when filed they are far too pink and I can't use them.

Where do I go now? I don't have the facilities or knowledge to do my own casting. Would commissioning a new set of castings using the sand casting technique be the way forward? If so I may need to modify some of the patterns to allow them to be extracted from the mould.

Here is a photo. The part-filed casting is on the left and a recently turned wheel blank made from cast yellow brass is on the right.

Edited By Nigel Watts on 17/12/2019 07:52:18

I wonder if the "yellow" that you see is an oxide layer formed as the metal cooled and that by filing that has been removed. It may return with time as the bare surface oxidises or may need to be encouraged by heating.

Have you contacted the company that did the casting to see what they suggest?

I emailed the supplier as soon as I realised to let them know I wasn't happy with the colour and asked whether there is another way of casting in which they could use the yellow clock brass (which they stock and sell on their website). I am waiting for their response.

This is the first time I have commissioned a casting so my knowledge is limited.

To the best of my limited knowledge, casting the yellow brass grades ‘in the open’ would contravene UK health & safety requirements ... which is why the trade was exported to India

The cost of doing the work ‘safely’ here is considered prohibitive.

MichaelG.

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https://www.hse.gov.uk/pubns/guidance/fd3.pdf

Edited By Michael Gilligan on 17/12/2019 08:35:34

Perhaps the foundry has an electroplating process that they use to get the proper yellow colour for clocks?

Whilst I generally agree that consistant colour material does help regarding looks you may well find that once polished the differences are not as noticeable.

regards Martin

I would need to send them back after machining and filing if this were the solution. The clock restoration purists wouldn't like it though. Being a valuable clock, I don't want to be too unorthodox in my use of materials.

You may be right but I am restoring a clock which could potentially survive a further few centuries. Differences in the composition of the alloys have a tendency to show up over time. I want to get it right, and the value and rarity of the clock means that I don't need to compromise if I don't have to.

I have contacted two more foundries and both say they can cast yellow brass, with one of them specifically saying he could do so using the lost wax process and describing what my founder had told me as "rubbish". I have still to hear from my original supplier. I am now more confused than ever!

Nigel,

I may be wrong, but please consider what I wrote in my previous post

It is my understanding that the viability of casting yellow brass [safely and legally] will depend upon what protective equipment the company concerned has available.

Your original foundry may not have made [excuse the pun] the necessary investment, but other specialists may have a suitable controlled environment.

i.e. both answers could be true.

MichaelG.

Good point. Thanks Michael.

It's hard too see why yellow brass, which seems to be a straight copper zinc alloy, would create any hazard different from other brasses. The hazard with straight brasses is with the zinc that tends to boil off and any brass foundry will be equipped to deal with this. Other brass alloys can contain lead or arsenic so I suppose these could pose different hazards. Perhaps the original foundry misunderstood the alloy requirement.

Rod

Interesting document here: **LINK**

http://www.hkramer.com/4KramerGoodFoundryPractices.pdf

Page 8 of which covers ‘leaded yellow brass’

MichaelG.

I've done some backyard brass casting. Bear in mind that (a) I do it outside and (b) the quantities are very small.

I learned quickly that the zinc can burn off but the bright flame and white fumes are obvious enough you should not get caught up in them if working outdoors if it catches.

I found that a generous dollop of borax worked as a cover flux and (mostly) prevented the oxidation/evaporation of zinc. Another tip I received was to add a tiny (~0.5% I think) amount of aluminium. You don't want much or it will become a horrible aluminium bronze.

Neil

I am not sure about foundries in UK or Europe but here in Ontario Canada several still are casting brass and bronze daily (and aluminum, and ferrous metal of course). I know of three foundries casting brass within 20 km of my town, I work with them in the day job. All do have good modern fume and particulate emissions control equipment, workers use proper PPE and respirators, but apart from that there is no magic and little hazard.

Nigel, neither of the two brass parts you showed look like casting would be a must to make them - could they not be machined from brass stock and surface-finished to look like castings if needed?

I made the part on the right in my previously posted picture (a clock wheel) from some cast yellow brass sheet sold specifically for antique clock restoration. I hammered it first to work harden before machining it using a wax chuck. I will be cutting the teeth using a fly cutter (the tooth shape on old clocks is pretty non-standard) before crossing it out. I included it its he pic as an example of the colour I need to match,

The piece on the left is the backcock from which the pendulum will be suspended. I agree that it, and all the other castings (see below) could be made in a different way - either cutting from the solid or fabricating by silver soldering pieces of sheet, but casting is the more authentic method and since I may wish to do this again in future i am keen to find a reliable supplier whom I can trust. The castings in the pic look pretty rough but that is because I made a terrible job of casting the waxes from my patterns and not the fault of the foundry who, apart from using the wrong metal, did a good job.

Edited By Nigel Watts on 18/12/2019 07:36:08

I get that you want the colour to be right for an old clock, but are you trying to pass off your newly made parts as being original to the clock ?

I would have thought it does not really matter if the parts are a slightly different colour, because they are obviously from recent restoration work and certainly not original, and as such will be part of its documented history.

If I were purchasing such a high value original item, I would not be too happy if i found out later someone had made most of it very recently.

Bearing in mind your comments about the value and rarity, are you trying to make the clock more saleable, or make it run better for years to come ?

Just curious.

Phil

Phil - what a good question, and one horologists can debate for hours on end!

My clock - a London made spring-driven clock by a recognised maker dating from 1710 - started off life with not only an hour strike, but also a quarter repeat mechanism (on the pull of a string) and an alarm. These clocks would originally have been carried around the house by a servant and placed next to the bed at night. In more recent times, such clocks ceased to be carried about and just sat on tables or mantlepieces and the quarter repeats and alarms fell out of use. Furthermore, the original verge escapements, which were so robust they could survive the moving about, also tended to get replaced with more accurate but more delicate anchor escapements. My clock, which I bought at a public auction, is missing its quarter repeat and alarm and has an anchor conversion.

Current feeling and practice amongst connoisseurs and restorers is that reconversion to verge and reinstatement of missing mechanisms is acceptable practice, as is trying to make the parts look authentic, including using the right colour brass (in fact not using the right brass is frowned upon). These clocks (mine included) don't just have ornate faces; the backplate and even some of the interior parts are ornately engraved, so its a bit like restoring a painting - all has to look right and blend in. I don't intend to sell the clock but in this internet age any knowlegable buyer would quickly be able to discover the auction catalogue listing and associated images of the clock in its unrestored state and deduce what had been done to it.

One thing I am being scrupulous about is making sure everything is reversible. This means using only the existing holes in the plates. Where these are threaded (and there were no standards in 1710), I will be making bespoke screws to fit. The only holes I will need to drill are where some original holes were plugged during the conversion to anchor. The main dilemma is to what extent should any remaining unused holes (mainly those drilled to fit the anchor mechanism) be plugged.

Nigel

What a good answer........I was rushing to type the question before dashing off to work this morning, and it was only with hindsight that I thought you might take it the wrong way.

I am into restoring early cylinder musical boxes and pre WW1 400 day clocks myself, and with the musical mechanisms there are many similarities to working on clocks, one such being the colour of the brass used for making parts, my musical boxes date from the mid 1800's up to Edwardian times, and the brass used was certainly more yellow than that available today.

I try and squirell away any old brass materials that I come across to use for for this purpose.

Likewise all my musical boxes and clocks are fully documented and photographed at every step of the restoration, I get great satisfaction from re-creating parts for something as old as these, but I am never going to kid anyone that they are totally original either.

Good luck with you brass hunt.

Phil