Leaded Gunmetal Are Typically 85% Copper, With The Balance Of The Alloy Made Up Of Of Tin, Zinc And Lead In More Or Less Even Proportions (Hence The Occasional Reference To The Alloy As An ’85/5/5/5 Metal’). Gunmetal Make Excellent General Purpose Casting Alloys, Lg2 Is The Preferred Version For Commercial Sand Founding, Lg3 For Art Founding. Lg3 Is Composed Of 7% Tin, 4% Zinc And 2% Lead, The Balance Made Up Of Copper (The Parent Metal) And Trace Elements. The Nearest Us Equivalents Are 844 & 836/C83500 & C83600 Alloys.
The Preference for Leaded Gunmetal (‘G’ Series Alloys) As Casting Materials Is Primarily Due To the Lead Bearing Material’s Superior Machining Qualities. Being A Relatively Soft Alloy, Leaded Gunmetal Permits an Easy Working of the Cast’s Surface during Chasing and Finishing (Some Founders Even Add in Extra Quantities of Lead to the Charge in the Furnace). The Addition Of Lead Does Mean That Gunmetal Does Not Weld As Well As Many Of The Other Copper Foundry Alloys And The ‘As Cast’ Surface Can Be Especially Dull In Appearance. A Decent Polish Can Be Achieved On Gunmetal, But Sculptures Which Are To Be Very Highly Polished May Be Better Formed From A Bronze (Copper/Tin) Alloy, Phosphor Bronze, Or Silicon Bronze; All Of Which Encourage A Brighter Finish – Though Even These Alloys Are Not Without Their Disadvantages (See Following Pages).
Whist the Lead Component Slightly Reduces The Weld Ability Of Leaded Gunmetal (Lead Can Increase The Incidence Of Gas Porosity In The Weld), The Material Is Still Quite Straightforward To Fusion Join. A Phosphor Copper Welding Filler Rod (Type C10 Or C11, Or Filler Compatible With C54400 Alloy), Flows Well And Has A Slight Degassing Action Which Can Help Reduce Weld Porosity. A Small Quantity Of Phosphor Copper May Also Sometimes Be Added Into A Melting Gunmetal Charge, This Helps Improve Flow And Reduce The Absorption Of Gases (Note: Silicon Bronze Should Not Be Added Into A Gunmetal Pot).
Using A Phosphor Copper Filler Produces A Welded Joint Of Considerable Strength In Gunmetal, Though The Quality Of A Newly Deposited Weld Run Can Be Further Improved By Lightly Hammering (Peening) The Weld’s Capping [Top] Run Whilst Still Warm. There May Be A Slight (Pinkish) Colour Variation In The Weld In Comparison To The Surrounding Parent Gunmetal; Any Obvious Difference Is Usually Negligible After The Application Of A Heavy Patina To The Cast.
The Welding Of Gunmetal Sections Is Normally Done With Tig, Or Occasionally The Oxy-Gas Process. Flux Coated Electrodes And Wire Fillers Are Also Available For Mma And Mig Welding Processes. A Very Limited Range Of Preformed Wrought Sections Are Available In Gunmetal From Specialist Stockholders, Usually In Lg2 & Nes 830 Grades. Wrought Gunmetal (In Common With Many Other Wrought Copper Alloys), Is Normally Sold In A Variety Of Imperial Sizes
Both Cast And Wrought Sculptures Formed In Gunmetal Readily Accept Standard Foundry Paginations; The Alloy Is Also Accept Gilded, Electroplated, Painted And Other Finishes.