New Delhi: Gold is considered to be the best option when it comes to investing or ornaments. What's good about the yellow metal is that it retains its value and is durable. However, buying gold jewelry can also be expensive. The price of gold varies greatly, depending on weight, karat and where you make your purchase. Because this special purchase is an investment that can last a lifetime, here are some tips which gives you insight into buying the precious metal: Every piece of gold should have a Bureau of Indian Standards (BIS) hallmark."The value of your jewellery is determined by the certification it carries. The Indian government has identified BIS as the sole agency for certifying gold," Calvin John, vice president (marketing) caratlane.com, said."Ensure that the gold jewellery you are purchasing has the BIS hallmark on it. The purity of coins and jewellery that is not BIS hallmarked may be questionable," he added.Gold is divided into parts to determine the level of its purity, which one needs to be aware of.Jewellery made of 24-carat (k) gold is pure or 100 percent gold. Pure gold is malleable and can be moulded with the bare hands.The Second category is 22k gold that contains 22 parts gold and 2 parts of additional metals, making it 91.6 per cent gold.It's popularly referred to as 916 gold.Then there is 18k gold. It has 18 parts gold and 6 parts of one or more additional metals, making it 75 per cent gold.The prices are decided according to the purity of the metal.Nowadays, most ornaments are made with 18k gold as it is relatively more durable against daily wear and tear, especially if it is studded with diamonds or gemstones.Kapil Narang, chief operating officer, Ameriprise India Pvt. Ltd, says if one is not buying hallmarked gold, one should rely on a trusted jeweller."Banks sell hallmarked 24.99 carat gold. If you are not buying hallmark gold, rely on a trusted jeweller or one who has long been in the market. One must also take into account associated costs like locker rentals, erosion and making charges. Lastly, keep in mind the ease of reselling," Narang said."If you are looking to invest in gold, coins are the best option as they offer liquidity, are accepted everywhere and are easy to store. Most people, however, like to buy jewellery as it offers the benefit of adornment while being a safe investment," he said.