Polishing - part 2
Continuing from last month, here are more tips on polishing your jade workpieces.
Hard felt wheels & points
Deborah Wilson in Vernon, British Columbia (BC) follows the “traditional” way of BC carvers in polishing. She uses a 200 mm diameter hard felt polishing wheel and 12,000 grit diamond paste at 3450 rpm and achieves fantastic results!
I agree with what she says - the felt allows more manoeuvrability of the workpiece than leather and quicker polishing as a result.
Avoid overheating the wheel by pressing for too long. Otherwise, the outcome, if not a burning wheel, will be white spots on your work caused by the nephrite overheating and some crystals breaking down into clays. I believe Deborah applies the workpiece for a maximum of three seconds before taking it off to cool for a few seconds (time to look at the finish) and then re-applies it to the wheel.
Deborah applies a coat of diamond paste to the new wheel and then allows it to be absorbed to some extent. With time and use it will become depleted, so more is added. See below for Deborah’s recipe for mixing her own paste.
Picture 2 on left - it shows my 150 mm diameter hard felt wheel, mounted in the drill chuck on my point carver. As you can see from the reminder written on it, I use only 14,000 diamond paste with it. You also see the syringe of paste and the small bowl of water used to cool work and fingers.
Tight corners can be polished by using a small felt point/tip or wheel fitted into your Dremel. Apply the diamond paste to the felt, press it in and add 2 – 3 drops of Chrystalube (a product made by Chrystalite described as “a silicone oil extender fluid and lubricant”) or other similar product to the tip or wheel, rub it in if it isn’t absorbed immediately and turn on the Dremel. The advantage of this type of product is you don’t have to use water, which would flick out anyway. It lubricates the process of polishing and extends the life of the diamond paste.
Picture 3 on left - shown are a selection of hard felt points and wheels, as well as a cloth mop, a couple of pieces of dowelling (the latter two discussed below) and a small mandrel, all useful in polishing tight corners.
Another method of polishing tight corners and small features is to use wooden tips impregnated with diamond paste. Small ones can be made from hardwood dowelling and inserted directly into your Dremel. Larger ones can be made from larger dowelling and either screwed onto a mandrel or glued with epoxy onto small steel shafts/mandrels. With the latter method you need to file and/or sand them down whilst they are turned in a chuck to make sure they are centred accurately.
You then use the diamond paste and a drop of Chrystalube and off you go. I run them at around 1000 – 1500 rpm – neither too fast nor slow.
A cheaper alternative to buying proprietary diamond paste is to make your own. Deborah uses the recipe shown below (and I thank her for allowing me to use it). The figures are shown as volumes, not weight.
Add 60% Vaseline to 40% lipstick (a cheap one or last year’s discarded fashion colour), mix with a small palette knife on a hard, flat surface like plate glass. Add the diamond powder as 25% of the lipstick volume and mix thoroughly.
Squeeze the mixture into a clean syringe purchased from a chemist or pharmacy. Try to avoid getting air bubbles in as you do so.
Each syringe should be labelled and kept separately, in a suitable plastic container with a sealable lid.
Rag-mop polishing wheels
You can use rag-mops (preferably stitched to make them more rigid) as a substitute for leather and felt wheels. They are generally sold without a mandrel but are quite soft so they don’t need to be accurately centred. They are not the best material to hold diamond paste though, but if they are all you can get, well, they’ll do!
Picture 4 on left - shown is my 150 mm rag-mop. I only use it with tin oxide - hence the note - memory is a wonderful thing! It is screwed onto a temporary mandrel, but could also be bolted onto a permanent one if I wanted.
They might instead be better to use with a polish like tin oxide on other types of rocks and minerals (one reference mentioned this being suitable for jadeite polishing though). The tin is applied as a slurry to the mop which soaks it up. It’s hard to dampen the mop. As a result, they produce a lot of dust as you use them (including the dried tin oxide) so you should wear a mask over your nose and mouth to avoid breathing it in too much.
Mini Flexodisc system
Another range of products made by Chrystalite are the “Mini Flexodisc” discs. They are hard rubber flat-faced laps attached to 1/8” (3 mm) shafts which come in three diameters – 0.5” (12 mm), 1” (24 mm) and 1.5” (36 mm), on which you mount self-adhesive backed discs made of cloth and a synthetic leather material of different grades of coarseness. They can be used (we are told!) with diamond (or corundum) compound ranging anywhere from 240 – 100,000 grit size and at speeds of up to 20,000 rpm. The company recommends using Chrystalube instead of water to lubricate the process, which makes absolute sense.
Picture 5 on left - shown are different components from the Mini Flexodisc system - the three differently sized mandrels with rubber pads and the three types of disc. It's all pretty self-explanatory.
The first (coarsest) type of cloth pad that you use is the Flexodisc, for sanding, cleaning up and shaping the workpiece. The next is made of a finer cloth for pre-polishing and is called a Chrystalpad. The third type is a Polypad, made of a synthetic leather-like fibre for pre-polishing and polishing and is to be used with 8000 grit and finer.
The manufacturer recommends using 325 diamond grit, followed by 1200 and then 8000 with the three grades of discs.
They are quite useful in some situations, but you must only press lightly on your work and keep the pads moving so as to avoid developing arc-shaped grooves. Practice makes perfect again!
So in summary, you can use whichever method of polishing you feel like. Different carvers achieve excellent results from several different methods and no one method is better than another. The main thing is getting the best out of your equipment and producing the best pieces you can through knowledge, practice and control. And did I say practice?!
11/12/2022 02:39:08 am
This is a great post thanks for writing it
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On this page I intend to add monthly updates on aspects of jade carving. I also plan to invite more experienced carvers to offer a "master-class" on a particular subject of their choice. With this I hope to enthuse both the novice and the expert in this ancient and beautiful art-form/craft. And comments are welcome!