Antiques are a special kind of decoration in FishVille, and currently you can receive them only as a gift. First we were introduced to the Vase. Then came the Ancient Urn, Ancient Helmet, and Greek Ruins.
So what is so special about the antiques?

They grow in value, and at a certain time, their value peaks. You also earn XP from selling them, which is different than a normal decoration. And after you sell an antique, you will also receive a bonus from the antiques dealer, which is a big reward.

OK so when you put an antique from your gift box into your tank, you will notice when you hover over it, that it shows a meter.

Aging:

The first section of the meter in orange is the Aging phase… this is where your antique builds in value. The arrow on the meter moves through here at a steady pace, anywhere from 30 hours to 120 hours.

Antique:

The second section of the meter is green, and is the Antique phase. This is where your antique peaks in value and is worth the most. You will notice that the value of your antique has jumped about four times what it was at the end of the aging phase. The value remains constant through this phase. The arrow on the meter will likely move at a different pace than before, because this phase is a shorter period of time, and a larger area of the meter.

You will know when it’s in the antique phase because the orange aging phase will be grayed out now. You may notice one, two, or three dollar signs on the meter, these are just for looks, and not an indicator of increased value or a bigger bonus. You will also notice that it sparkles now, and that there is a little barnacle symbol on it. So far, the different barnacles haven’t been an indicator of the bonus.

Decay:

The third section of the meter is the Decay phase, this is where your antique will decrease in value alot initially, and at a steady pace as well. Just the opposite of Aging. And you will not receive a bonus anymore from the antiques dealer. It will grow ugly barnacles on it. You can clean it during this phase, but it will not return to the Antique phase or it’s full value. Eventually when the meter runs out it turns to “Junk!” and is worth only 1 coin & 1 XP.

Cleaning:

You will notice after a little while in the Antique phase, if you click on the antique, next to the “Sell” button the “Clean” option is now available. Cleaning your antique resets the Antique phase. It doesn’t affect value or bonus. It gives you another 24 hours for you to decide whether you want to sell, or keep it in your tank. Oh and cleaning earns you +3 XP.

Bonus:

OK so what is so great about antiques? Well when you sell them during the Antique phase, you receive a bonus from the antiques dealer. You can earn coins, XP, or a sand dollar.

The coin and XP bonus are determined by your level. You earn anywhere between 10 and 25 times your level. So if you are level 10, the lowest coins or XP you could be given as a bonus would be 100, while the highest would be 250.

You can also be given a sand dollar if you are lucky. Right now the chances of that looks about 1%.

The Different Antiques:

Each antique has a different aging schedule, and different values as well. Their bonus appears to be the same, but I could be wrong (you aren’t more likely to get a sand dollar from a greek ruin than an ancient urn).

Ancient Urn: – Gift
Aging Phase = 30 hours
Antique Phase = 12 hours
Maximum Value = 287 coins & 11 XP + bonus

Ancient Helmet: – Gift
Aging Phase = 40 hours
Antique Phase = 15 hours?
Maximum Value = 311 coins & 12 XP + bonus

Vase: – Gift
Aging Phase = 60 hours
Antique Phase = 24 hours
Maximum Value = 1285 coins & 51 XP + bonus

Antique Statue: – Gift
Aging Phase = 60 hours
Antique Phase = 24 hours
Maximum Value = 5694 coins & 228 XP + bonus

Cherub Statue – Gift
Aging Phase = 60 hours
Antique Phase = 24 hours
Maximum Value = 17405 coins & 696 XP + bonus

Greek Ruins: – Gift
Aging Phase = 78 Hours
Antique Phase = 30 hours
Maximum Value = 4184 coins & 167 XP + bonus

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So far the following look like they have a 30 hour Aging phase

Broken Column – Gift
Aging Phase = ?? hours
Antique Phase = ?? hours
Maximum Value = ??? coins & ??? XP + bonus

Greek Scale – Gift
Aging Phase = 35 hours
Antique Phase = ?? hours
Maximum Value = 2504 coins & 100 XP + bonus

Grecian Urn – Gift
Aging Phase = 35 hours
Antique Phase = ?? hours
Maximum Value = ??? coins & ??? XP + bonus

Neptune’s Trident – Gift
Aging Phase = 35 hours
Antique Phase = ?? hours
Maximum Value = 3214 coins & 129 XP + bonus

Metal Pipe – Store
Cost = 2400 coins
XP Bonus = 24 XP
Aging Phase = 35 hours
Antique Phase = ?? hours
Maximum Value = 2641 coins + bonus

Rusty Anchor – Store
Cost = 2300 coins
XP Bonus = 23 XP
Aging Phase = 35 hours
Antique Phase = ?? hours
Maximum Value = 2530 coins + bonus

Sunken Bell – Store
Cost = 4900 coins
XP Bonus = 49 XP
Aging Phase = 35 hours
Antique Phase = ?? hours
Maximum Value = 5390 coins + bonus

Neptune – Store
Cost = 15 sand dollars
XP Bonus = 750 XP
Aging Phase = ?? hours
Antique Phase = ?? hours
Maximum Value = ??? coins & ??? XP + bonus

Credit (Source)