The purpose of insuring antique item is that you should receive the insured value in case of total loss.
However, before paying you the insured amount, the insurance company will ascertain the market value of the antique items. They will do this by getting the value certified by a panel of antique dealers or appraisers.
The amount paid to you will be based on the estimate submitted by these estimates. In case you are not agreeable to the value of your antiques; you can raise a dispute and go in for a dispute resolution process as per the terms and conditions given in your policy.
For this you might be required to get your appraisal from recognized antique appraisers. This should be comparable to the stated value in your policy.
Your agent or lawyer need to establish that the appraisal marches the stated value of the antique items. The actual value of the antique items can be speculative, so you must have strong evidence to back your claims.