Not technically a "write-off" unless you are in the trade or business of buying or selling bullion. But if you had to pay direct storage fees for these items, you may be able to add those costs to your cost basis (which would then reduce your gain upon sale). Similar to adding cost of home improvements to the basis of a house you have sold. But the indirect overhead costs such as electric and mortgage interest are a little more questionable.
Well, I got that straight from an example in an IRS publication. Don't have the time at the moment to look it up again though. Okay, took a minute to look up the publication again. In IRS Publication 550, Investment Income and Expenses, under the section entitled "Capital Gain Tax Rates", is the following example ... Example. All of your net capital gain is from selling collectibles, so the capital gain rate would be 28%. Because you are single and your taxable income is $25,000, none of your taxable income will be taxed above the 15% rate. The 28% rate does not apply.