How Much Loss Can One Expect from Evaporation of Metal in a Pour?

Actually Michael, There is no loss from evaporation in the melting and pouring of gold ( or any precious metal for that matter) - what may happen , if using an old crucible that is gunked up with visible oxide containing borax glaze is that a few grains or spheres may stick to the borax from the glazing cooling before the metal is completely poured. The internal crucible area may appear reddish brown or green-blue depending on the Oxy/Fuel torch you use and the metal you are melting.Silver, .925 containing a high copper content relative to the sterling alloy will be more blue-green from cupric oxide(s), whereas high karat yellow golds will appear reddish brown or brown due to the fine silver content reacting with acetylene or propane due to the absence of copper or lower Cu content until you get to high copper containing alloys such as 9-14 karat golds. Whilst pouring keep the reducing flame ( a bushy blue flame as opposed to a hissing sharply pointed blue in deep blue flame) concentrated on the metal in the crucible. Gold is not a gas and neither a liquid so there is no evaporation from the metal to worry about. You can visually inspect the crucible for the small spheres of gold after a melt and remove them by breaking the pieces out of the glaze the glaze or warming it and removing them with tweezers.Spilled metal is easy to spot in the vessel you use for holding the mold.Generally a little will collect around the base of two part clamped type molds since there is usually a thousandth of an inch or so gap that is normal for molds that are hand assembled: even though the metal parts may seem truly square after use and repeated lubrication there is some seepage to be expected from a build-up of wax, oil or synthetic lubricants at which area the the plates join.I would not advise removing that "seasoning" as it helps the pour relaaese a brighter tougher ingot or rod from repeated healting and cooling of the steel used in its construction: much like a treasured cast iron kitchen skillet- that seasoning helps metals relaese easier just like foods release in a skillet that is well seasoned r and cleans up with only scalding water . If you do at some point remove any excess "pooled" lubricant material toss it into the scarp refining bin as it will contain some micro-particles of gold, or whichever precious metal you dedicate the mould to.Remember to pickle those bits as they are quite oily from whatever lubricant you choose to use in pre-heating your mould instead of just tossing it into the scrap container for the next pour, or for a small piece to use as an accent in a design because the oils will prevent the solder from flowing properly regardless of the flux that is chosen, or the metals to be joined. The best practise though is to use a new fused silica crucible.( a "burn-o" type with a high back wall and a pour spout works well for hand pouring).Be sure and use sturdy tongs intended for the purpose that cross-lock for holding a crucible securely. Avoid bar-b-que type or kitchen tongs.The best tongs are about $4.00 from most vendors. Warm it. Then put about two tablespoons of pure borax in the crucible and with a hot torch melt and swirl the borax to completely cover all surfaces of the inside of the crucible and if a pouring hole exists, try to get a small amount to glaze that too ( that is where most will become trapped in subsequent uses as the hole is often too small and the metal cools in the thick borax glaze). It will appear glass coated and is ready to take your scrap or casting grain at that point. Be sure all solder is removed from scrap before melting - it will contaminate your ingot or bar and cause many problems that are easily avoidable by running a magnet over your metal first, and insuring to inspect jewelry scrap you did not make for hidden solder joins around bezels, at clasps, and in settings. If there is any loss it can usually be reclaimed if you put your mold in an iron skillet filled with powdered charcoal, crushed lava or other refractory rock, sand or other grain that will both stabilize the mould and make it easy to spot drips or other escaped particles. Always grease or wax your mould before pouring and insure that it is at least warmed.I use a crucible for 22 and 24 karat pour that has a hole in the back and whilst heating the crucible and melting the metal flames automatically shoot out the hole and I position it so it heats the mould at the same time.Never get water in the crucible and store it when cooled as dry and humidity proofed as is possible. I use a different crucible for golds and silvers, and never mix .999 silver with .925, likewise do not mix 14 karat ( which i use only for parts that take stress such as clasps etc.) or other copper containing gold alloy combinations with high karat golds.Platinum and white gold get their own crucibles and since white gold in all karats contains nickel, it doesn't need different crucibles for different karats. I do hope this answers your question and accept my apologies for the length of time it took to find your email as there has been some illness in my family that required my attention away from the computer. Best Regards, Ari