Our raw material and starting stock inventory is primarily comprised of ferrous and non-ferrous scrap metal and alloys such as nickel, chrome, molybdenum, cobalt, vanadium and copper. Our semi-finished and finished steel products are work-in-process in various stages of production or are finished products waiting to be shipped to our customers.

Operating materials are primarily comprised of forge dies and production molds and rolls that are consumed over their useful lives. During the three months ended March 31, 2020 and 2019, we amortized these operating materials in the amount of $0.6 million in each period. This expense is recorded as a component of cost of products sold on the consolidated statements of operations and included as a part of our total depreciation and amortization on the consolidated statements of cash flows.

Inventory is stated at the lower of cost or net realizable value with cost principally determined on a weighted average cost method. Such costs include the acquisition cost for raw materials and supplies, direct labor and applied manufacturing overhead. We assess market based upon actual and estimated transactions at or around the balance sheet date. Typically, we reserve for slow-moving inventory and inventory that is being evaluated under our quality control process. The reserves are based upon management’s expected method of disposition.

	March 31,		December 31,
(in thousands)	2020		2019

Raw materials and starting stock	$	11,108	$	9,815
Semi-finished and finished steel products		125,880		127,713
Operating materials		13,126		13,090

Gross inventory		150,114		150,618
Inventory reserves		(3,335)		(3,216)

Total inventory, net	$	146,779	$	147,402