March Meeting The Restoration and polishing of Slate Clock Cases By visiting British Horological Institute member B.LINES (MBH)

Transcription

1 March Meeting The Restoration and polishing of Slate Clock Cases By visiting British Horological Institute member B.LINES (MBH) A few words about myself and how it all started, there are proprietary products on the market for slate case restoration (e.g. Meadows and Passmores slate blacking. Some people use black shoe polish. I have even heard of people painting or lacquering the slate cases. Some of these products do have a use in the right circumstances. But they don t remove the corrosion, all they do is to partially cover up the white or grey and bring some sort of shine. They do nothing for the gilt patterns or the repair of broken corners and you cannot use them on coloured inlays or marble pieces. Some of you may have restored slate cases before. If your method works then carry on. The method that I am going to show you may involve some skill some hard work but at the end of the day it works and the results are very good Is it Slate or Marble??? Marble? - Marble is a metamorphic rock, heat and pressure changed Limestone into a crystalline form of Calcium Carbonate. It reacts with dilute acids to give the calcium salt of the acid plus several volumes of Carbon Dioxide gas. This is how you can test if it is marble? From an eminent Geologists point of view the black cases are a type of Limestone. There has been no heat and little pressure applied therefore only small changes to its structure. BUT I still call them Black Belgium SLATE Clock cases and even that s still not quite right. Firstly Safety If you are grinding use safety glasses or goggles Do not inhale the dust produced its bad for the lungs it could be poisonous keep the dust down it is best to The Process Is Broken Down Into the Following Sections 1. Taking the case apart 2. Repairing the broken corners 3. Restoring the gilt patterns 4. Replacing missing stone inlays 5. Polishing the pieces 6. Assembling the case 7. Final finishing 1 Taking The Case Apart Study the design and how it was originally assembled. Are there any sub assemblies? (e.g. the central box for the movement.) Are there metal or marble columns held (together with long threads and nuts) The base and where its break line is.

2 That Completes the Dismantling of the Case Remember NEVER Directly Hit the Slate or Marble With a Hammer 2 Repairing the Corners Taking the case apart is not always necessary. You can sometimes stone the broken corner flat, stick on a new piece, shape and polish it all without taking the case apart.

3 The surfaces that are to be stuck need to be flat (very flat) the glue line wants to be only 0.04mm (2 thou) thick. Please take great care with this part For Sticking the new corners on permanently I always use the original STANDARD ARALDITE not the RAPID - It takes approx 24 hours to fully cure The corner is partially finished with 400 or 600 grit paper and left for later finishing Occasionally you can get round the problem of chipped corners by putting a radius on instead. You have to then do the same to the other corner/s so that the case looks symmetrical, and you still have to polish anyway 3 Restoring the Gilt Patterns Generally you have two options. A Using a Gold Paint B Using Gold Leaf They both work and each has its own advantages and disadvantages Gold Paint This is completed in three stages (a) Cut the pattern deeper (b) Fill with paint and let dry (c) Remove the excess paint and the old corroded surface Remember - Use many light strokes and not heavy ones

4 Remove all the white / grey corrosion with 320 or 400 grit paper. It may be necessary to cut the pattern deeper and repaint again to remove severe marks. Finish all pieces with 400 or 600 grit paper. Using Gold Leaf This is completed in four stages (a) Cut the pattern deeper if the surface needs polishing or clean out any old dirt /leaf etc (b) A light coat of size (adhesive) (c) Add the leaf and push into the pattern (d) Remove the excess Gold Leaf and excess adhesive The clock case finished with 400 or 600 grit paper all over. (except the back)

5 4 Replacing the Stone Inlays The Dust from the stone inlays are generally Irritants some may be a little Poisonous. Some people may be very sensitive to it. Do not inhale the dust. Most of the inlays are very brittle or have weakly bonded layers. With care you can cut, grind and shape the inlays. If you break one simply glue it back together and carry on.(with more care) To stick the inlays in A) Take a scrap piece of inlay material grind / crush it to a fine powder. B) Save some small pieces to fill the gaps or broken corners Mix 50% ground dust with 50% Araldite adhesive. Use this mixture to stick the inlay to the clock case. If necessary push some small pieces into the adhesive to fill the gap Allow the glue to cure hard. Then with care reduce the excess material down to the level of the face.

6 As with the rest of the case finish the surfaces with 400 or 600 grit paper for later finishing 5 Polishing the Pieces Before you start polishing CHECK Are the corners repaired and finished? The Gilt patterns repaired and finished? The stone inlays repaired and finished? The Basics You use progressively finer papers to remove the scratches produced by the rougher paper used before. 600 to remove 400 grit scratches. 800 / 1000 to remove 600 grit scratches. Finishing with 1500 grit paper. You must keep the pieces clean. Every time you change papers wash - rinse the part of the clock. You also wash and rinse the new finer piece of abrasive paper to remove any stray grit. The whole clock all the faces / pieces that need polishing should be worked upon by one grade of abrasive paper at a time. You then Clean it all thoroughly and carry on with the next finer abrasive paper. There is one thing I cannot stress enough. Keep it clean. If you don't all your hard work will be wasted and you ll have to do it again. In the Victorian times they originally used ROUGE IRON OXIDE. Later they used TIN OXIDE Today - The final polish is produced by using CERIUM OXIDE on a suitable backing. Cerium Oxide is a fine pale pink powder. You mix it with water to a thick creamy consistency. You apply it to a suitable backing e.g. Leather (suede), Cork, Soft wood, Hard felt and many more. The polishing effect is produced by the friction / rubbing action of the object against a suitably charged pad of Cerium Oxide. The process is called vitrification (to produce a glass like surface) If the Cerium oxide is too wet there is little or no polishing. If it is too dry it tends to burn and stick to the surface again with no polishing. There is a part between where it drags and pulls and gives the best polishing It all happens at the molecular level by fusing the structure together. Its thickness is probably only a millionth of a mm or less. I m afraid the only way to find out is to actually try it.

7 It s a sense of feel just how the polishing is going. Once the required finish has been obtained clean all the pieces. Paying particular attention to remove the polishing powder from the gilt pattern, stone inlays and the marble pieces. 6. Assembling the Case There are several suitable adhesives (1) POLYFILLA for the case (2) Fine Tile Adhesive for the case (3) Plaster of Paris for the case (4) Plaster of Paris for the wires You must never use any permanent adhesives like Bostik contact adhesive, Araldite or any other Epoxy based two part adhesives for the case assembly. Generally the first piece to be assembled is the movement box to the base. Apply Poly filla adhesive to the box, align the box evenly with the base and let it dry. Carefully place the wires that hold box to base and cover them with a dollop of plaster of Paris The next parts are the top plate and the top ornament These are stuck with Polyfilla Carefully wipe off any excess adhesive with a damp cloth Dry for two days or longer There you have it Nicely repaired, restored, polished and assembled All it needs now is final finish 7. The Final Finishing First. Where Polyfilla was used a white join line can be seen between the parts. This can easily be disguised by the use of Black Shoe Polish Use an old tooth brush and rub it along the joins then polish off the excess when dry with a polishing cloth. But only use it on the join lines. The final finish on the case is a coat of good quality clear wax. Coat the case with wax using a clean cloth. Then with a hot air gun gently warm the wax and the case. This causes the wax to melt and seep into the microscopic cracks and cavities in the case and fill them. When using the hot air tool caution is required Do Not play the hot air on the gilt patterns it will burn them off. Don t keep the hot air gun in one spot for any time. The excess heat could crack the slate. Don t get the case too hot you will soften the internal glue causing serious damage. When cool all the excess wax is removed with a polishing duster. This leaves the case with an even colour and shine. The wax in the pores protects the surface from further corrosion. That just about covers the case polishing and restoration.

8 I have a few more slides showing how the same techniques can be used on Marble and other Slate cases. So where do you get the pieces of marble from to match the case exactly Green Marble Case with missing edge With this case there are no spare pieces within the structure. The best place for small pieces of marble especially Green Onyx type of stone are garage, car boot sales and auctions. One Point to Remember To restore Black Slate or Marble cases properly takes between 15 and 40 hours or longer. Sometimes the clocks are only worth a $ Hard work but the results are worth it. Thank you for inviting me along Thanks to Brian (aka Sid) Lines for his time and sharing his method of restoration with the members of the AAHS