Pāśupata-vrata Māhātmya: Dvādaśa-Liṅga Mahāvrata, Month-wise Dravya, and Pūjā-krama
रत्नानाम् अप्यलाभे तु हेम्ना वा राजतेन वा रजतस्याप्यलाभे तु ताम्रलोहेन कारयेत्
ratnānām apyalābhe tu hemnā vā rājatena vā rajatasyāpyalābhe tu tāmralohena kārayet
If gemstones are unavailable, one may have it made with gold or with silver; and if even silver is unavailable, then one should have it made with copper or iron, so that the worship of the Liṅga of Pati (Śiva) is not obstructed by lack of materials.
Suta Goswami (narrating Shiva-puja vidhi as received in the Linga Purana tradition)
It establishes an authorized hierarchy of substitutes—gem, gold/silver, then copper/iron—showing that sincere Linga-puja should continue even when ideal materials are not obtainable.
By allowing substitutions, it implies Śiva as Pati is not confined to a particular substance; the Linga functions as a supported focus for devotion, where bhakti and right procedure matter more than luxury.
A practical rule of puja-vidhi (dravya-vikalpa): ensure continuity of worship by making or commissioning a Linga from available metals, removing external obstacles that can bind the pashu through pasha (limitation and neglect).