Modern dial salts are very mean with the sliver and leave a stainless steel, or burnished aluminium [sunburst] look. Which is completely and utterly wrong on an old, antique dial! So avoid eBay or Meadows and Passmore's "finest" "Horrorsilv" silvering salts if you are not to be sorely disappointed! Or want to be instantly recognized as a clock botcher [never bodger] by any self-respecting clock restorer!
I have silvered dozens of antique, brass, clock dials myself so know the difference. The proper white salts are still obtainable and are head and shoulders above the modern stuff. I have both kinds in in my cupboard and enough self-respect to know which is which. I recommend Holtby's silvering salts as a highly satisfied user with no commercial interests.
Note that a matt white dial drastically improves legibility of the digits, clock hands and any engraving on a brass dial. They literally jump out at you compared with modern, shiny and silvery finishes. The latter greatly reduce legibility. Even by adequate, modern, artificial light the time on a polished dial is hard to read because it reflects what is in front of it. Try reading such a dial with a torch or candle from a distance!
Avoid the nasty, modern silver salts like the plague as they do produce a horrible shine which is highly undesirable. There should be no shine at all on a properly silvered dial! This is quite deliberate.
Matt white looks instantly and magically gorgeous during the silvering process. Which was perfected centuries ago when light, after dark, was usually in very poor supply. The only clock in the house usually had to be legible with just a distant and sputtering candle, or taper, from the far end of the hall. Or the cows would not get milked. Nor the household fires lit. Nor the horses harnessed. These were vitally important matters at the time. An hour, in the pitch dark, is a very long time to wait, turning restlessly, between the regular, hourly strikes of a clock's bell.
Silvering is a simple enough task with the required salts and only involves wet rubbing of the brass with fine [wet and dry] emery paper to clean back to bright brass. This is known as graining and coarse abrasives must be avoided at all costs or the dial markings will soon disappear completely!
Try selling your Tompion without a signature or its exquisite dial markings! I have even seen early 18th century clock dials in historical period TV programmes with shiny dials. It is so out of period and character that they might as well have put a baseball cap on the heroine! 😲 Even stately homes and museums have had their valuable clock dials brightly silvered by a Meadows & Passmore wielding vandal! If it's not flat white it's not real! It's as simple as that.
Graining is often accomplished with a manual, rotary action involving a cork sanding block [for the 400 grade emery paper. With a couple of drawing pins for security] on a simple arm with central pivot. The dial is usually supported on a heavily drilled board to allow the dial feet to sink. Allowing the dial to lie flat and stable as the block is rotated back and forth.
The block, or pivot radius must be adjusted to match the dial, or chapter ring size. I had a series of holes in the radius arm and just moved the cross-pin along as required. The emery papered block must be lifted clear when finished with the graining. Or smudging of the circular grain will easily occur. Vertically graining, a one piece, regulator dial requires lots and lots of patience! Don't try to circularly grain a one piece dial or it will look like it came in on the last boat from China.
Graining is immediately followed by rinsing well under the cold tap and then cleaned off with bare, wet fingers but not dried.
This is quickly followed by damp rubbing with the correct [white] silver salts using one's bare [and perfectly clean] finger tips. Small cuts may sting but I have never been poisoned by the silvering process. Some people like to use a rag for rubbing the silver onto the clean brass.
The silver should soon appear as a [sometimes] rather dirty but solid white. It should only be rinsed off when satisfied that a good and even coat of silver is in place. If not, just add more silver salts and rub some more with clean, wet and bare finger tips.
Note that each stage ensures the fingers/hands never dry off so they never have a chance to get greasy or oily. Silver will only adhere to perfectly clean metal. So finger prints will show up if allowed to spoil the clean, wet brass. They may even show up much later. Long after you have delivered the clock to a valued customer 100s of miles away!
The silvering stage is finally neutralized and whitened further with ordinary, household, Cream of Tartar powder rubbed on damp over the fresh silver coating. Followed by plenty of rinsing. I found some finishing powders shine far too much when I was re-silvering antique clock dials. Modern and unnecessarily expensive finishing powders will easily spoil even the correct white silver salts! So buy Cream of Tartar powder cheaply from the supermarket instead.
Clear lacquering is normal for dials which are regularly handled for resetting to time. That means most longcase clocks and those which need a winding key to be guided through a small hole.The main problem is the wax filling in the engraving can become dissolved by the clear lacquer's own solvents. So that they later bleed dark marks into the surrounding silver.
If you can keep your fingers well clear of a bare silver dial it should last quite a while before re-silvering. Though this is not acceptable for a customer's clock. You never know who will be asked to wind it or will try to reset it to time.
Re-waxing the engravings of a brass dial or chapter ring is quite another matter and should not concern the WT owner needing a simple, time-setting dial 're-freshening' of the silver.
BTW: Avoid heating any antique brass dial unduly. They tend to off-gas which used to be highly toxic when I still worked on lots of clocks. Overheating caused me instant asthma. Though I do not normally suffer from asthma, at all. Interestingly WD40 has very similar toxic effects on me but many swear by the product and use it for everything. WD40 puts me in bed to recover if I so much as get a whiff of the stuff! The same with old dials while warming them to re-wax the engravings.
There is a tradition that antique brass dials are not chemically cleaned on the back. As if it added some 'hazy' authenticity to the countless "marriages" purveyed by many in the [antique dealer] criminal classes.
I did plenty of work for a major, rural, clock specialist. He would regularly play mix'n'match [i.e. mismatch] with longcase weights and pendulums entirely at his personal whim. Anything to make a few pounds more on a smarter clock. I was expected to make them fit somehow until I grew tired of his corruption, greed and idiocy.
I called a complete halt when he demanded dials were swapped with movements purely for profit. A so-called marriage. Easily done, but it requires new holes are formed for the dial feet and the old ones disguised with brass disks hammered in to disguise their presence. This was a common ploy with nice, 30-hour cases needing a [usually much younger] 8-day movement to sell for umpteen extra thousands to uncaring philistines just looking for a furnishing piece. There is no way back from a bad marriage. Of any kind!