Metallurgy Question:

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Porosity is related to air or gas entrapment during the melting or casting process. When the metal cools and solidifies a small hole is left in the casting. Good out gassings of the melt and good foundry practice can eliminate much of this. Porosity can also be caused by lack of flow into the mold, which is a function of the alloy, superheat (temperature above the melting point), complexity of the mold and a few other factors. Another problem might be entrapment of impurities or slag in the melt. This results in a "dirty" casting. Some aluminum alloys can be particularly prone to these problems. Porosity can be eliminated by careful slag control in the melt, filters, and pour techniques.

I am not sure if the problems are particularly Indian versus British but the people who are doing the casting. I have seen excellent Indian, British, U.S., and Mexican castings as well as bad ones for these nations.