From the query raised, it is not clear, at-least to me, that whether contract with Anderson Inc, Germany is for two items i.e. (casting as well as patterns) or only for just one item (i.e. casting) wherein cost of patterns are shown separately so as to arrive at full purchase price of casting so ordered.
Let me try to answer the query in both scenarios:
A. Scenario No. 1: Contract with Anderson Inc, Germany is for two items i.e. (casting as well as patterns):
A1. Value of taxable supply for 'Castings' will be ₹ 2,10,000/- (i.e. including cost of patterns) u/s 15 of the CGST Act, 2017. However and as subject castings are presumably getting physically exported out of India, then, such supply will be zero-rated u/s 16 of the IGST Act, 2017. 'Value' u/s 15 will not matter much when supply is zero-rated.
A2. But, the supplier needs to pay applicable GST against 'Patterns' as same is sold to Anderson Inc, Germany but not physically exported out of India.
A3. In such a case, 'Pattern' will not be asset for the querist as same are goods owned by Anderson Inc, Germany but only physically kept with the querist.
B. Scenario No. 2 - Contract with Anderson Inc, Germany is for one i.e. casting, wherein cost of patterns are shown separately so as to arrive at full purchase price of casting so ordered:
B1. Value of taxable supply for 'Castings' will be ₹ 2,10,000/- (i.e. including cost of patterns) u/s 15 of the CGST Act, 2017. However and as subject castings are presumably getting physically exported out of India, then, such supply will be zero-rated u/s 16 of the IGST Act, 2017. 'Value' u/s 15 will not matter much when supply is zero-rated.
B2. But, as there is no supply of 'Patterns', question of paying GST there-against does not arise.
B3. In such a case, 'Pattern' will be asset for the querist as its ownership is not transferred to Anderson Inc, Germany.
On parting note:
As said earlier, essence to answer your query, to my mind, is determination of the fact that whether Anderson Inc, Germany is raising order for two items i.e. (casting as well as patterns) or only for one item (i.e. casting) wherein cost of patterns are shown separately so as to arrive at full purchase price of casting so ordered. Without this determination from contract / PO and mutual understanding etc., I think it is difficult to conclusively answer.
Above are strictly my personal views and same should not be construed as professional advice.