Brass is an alloy of copper and zinc. Bronze is a metal alloy consisting primarily of copper, usually with tin.

Tin resists corrosion from water, but can be attacked by acids and alkalis. Tin can be highly polished and is used as a protective coat for other metals.[6] A protective oxide (passivation) layer prevents further oxidation, the same that forms on pewter and other tin alloys.

The tin has been added to inhibit dezincification (the leaching of zinc from brass alloys) in many environments. This group has low sensitivity to dezincification, moderate strength, high atmospheric and aqueous corrosion resistance and excellent electrical conductivity. They possess good hot forgeability and good cold formability. 

 

Bell metal of Mannar https://www.keralatourism.org/kerala-article/bell-metal-mannar/86

A unique metal which is a harmonious blend of tin and copper, bell metal reflects the elegance of a craft, the tradition of which dates back to several centuries. Typified by its sonorous quality when struck, bell metal provides a fine medium for the craftsmen to cast both religious artifacts as well as domestic utensils.

Mannar, a small town by the side of Pampa River between Mavelikkara and Thiruvalla in Alappuzha district of Kerala state, is well known for its association with bell metal. Mannar has been in the mercantile maps of Kerala for quite a long time. Take a stroll through the comforting constrains of this Bell metal town and soon you will observe all your attention being absorbed by the gleam of bell metal utensils.

Crowded with an assortment of traditional alas or forges Mannar has been engaged in this business for centuries. The artisans of these alas produce an array of bell metal products that include household utensils like Uruli (a wide mouthed vessel), Nilavilakku(a wick lamp), Kindi (a spouted pitcher) and idols of Hindu Gods like Lord Shiva, Lord Krishna and Goddess Lakshmi. These elegant artifices over the years have crossed the Arabian Sea to spread the fame of this small town and to capture a range of markets in different parts of the world.

http://www.indiastudychannel.com/experts/40283-What-is-bell-metal-What-are-its-uses.aspx

Bellmetal is an alloy of Copper and Tin. It is a variety of Bronze(copper-tin alloy) with 78%-22% copper-tin combination. It is used for making bells as the particular combination gives strength and not easily giving for abrasions. This combination gives a particular 'clang' sound clear and distinct and reverberating, so it is used for bells.
The other variety of bronze is the white bell metal which has still more percentage of Tin in it. Vessels made of bell metal (or 'Vengalam' or Vellodu in Malayalam) were and still to some extent commonly used for cooking items like Payasam(Kheer) or boiling milk in temples and other big social functions in Kerala. They are less corrosive and less prone to abrasions in comparison to brass and copper vessels. While brass vessels and copper vessel become corroded and get the 'verdigris', bell metal or white bell metal vessels are not prone to catch verdigris*. They are commonly used in temples and homes for puja purposes and also cooking, and for making Ayurvedic medicines which need long time heating and boiling.
*(verdigris is the dark green or bluish green colour formation on the surface of brass and copper vessels exposed to air and humidity.)

As knowledge about metal and alloys are known to humans, even bell metal is produced in other countries, and in many places in our own country. However craftsmanship, unique methods of making and polishing etc make each one famous in its own way. For example in Kerala places like Nadavarambu, Mannar etc are more known as there are certain traditional families who have the expertise coming from many generations.

Bronze/bell metal is used for making cannons due to the strength and less corrosiveness it offers. 
Variation in combinations, different shape, thickness or hollow all can affect the sound coming from a metallic product.

 

Source

Ananthoo - good on bring mud back http://ananthoosupdates.blogspot.com/2016/06/bringing-mud-back-event-at-chetpet-1112.html 

http://easyayurveda.com/2014/01/22/cancer-ayurvedic-understanding-hopeful-treatment-modalities/#comment-22560

http://www.thehindu.com/news/cities/chennai/why-does-rasam-taste-the-way-it-does/article3001718.ece

https://www.youtube.com/watch?v=Wh0gh1h4QrI

http://intangibleheritage.intach.org/history-of-tin-coating-of-metallic-utensils-in-india/

 http://www.thanjavurparampara.com/single-post/2015/07/29/Traditional-Cooking-Vessels

 

 

rajiv says:

Sir, good to see ayurvedic doctors advocating organic food. Also we must avoid processed food stuffs like ‘table salt’, ‘white sugar’, ‘white polished rice/maida’, ‘refined oil’. Better to stick with raw sea salt, Jaggery powder and full rice and full wheat atta, cold-pressed oil. Ayurvedic doctors must also advocate healthy cooking utensils. Nowadays all our traditional cooking utensils have disappeared and replaced with toxic Stainless Steel, Aluminium, and newer vessels from the west have even more toxic coatings like Teflon,etc.

Even most of the Ayurvedic medicines today are cooked in stainless steel vessel. Depending of the grade of stainless steel, it contains alloyed amounts of Chromium and Nickel with Iron. Chromium and Nickel both are very toxic. While Stainless steel is a wonderful metal for industrial applications it should be kept away from the kitchen or even if used in kitchen it should be coated with a layer of tin like traditional vessels.

Our traditional vessels for cooking food consisted of
1) Pure Copper vessel: Used to boil and store water. Even today most temples store water in copper vessel only. Copper is also one of the best conductors of heat and hence water boiled in copper vessel has a very pleasant taste, unlike water boiled in Stainless Steel vessel. Copper though can’t be used for cooking food as the metal corrodes when it comes in contact with food.

2) Bell Metal or Bronze: Most famous is ‘uruli/vaarpu’ cooking vessel from Kerala. Besides Kerala, Assam, Odisha also famous for traditional Bell meal. Tamil Nadu also famous nowadays for making brass/bronze Pongal vessel. Bell Metal is made from mainly Copper and with alloying of Zinc+Tin and maybe small amounts of lead+mercury(not sure about composition as the bell-metal makers usually keep composition a secret. Besides the metals certain barks also used in metal making). Of course Lead+Mercury when alloyed with Copper in very small amounts generally not toxic.
Bell metal ideally suited for making semi-dry items in water-based cooking/steaming like Pongal/Khichdi/Upma/Idly. Also ideal for making Ayurvedic Lehyas like Chyawanaprasha.
Bell Metal can also be used for frying. I’ve seen traditional Bell-Metal frying vessels from Andhra Pradesh.

3) Tin: Usually Tin-coated brass vessels used for water based cooking i.e making soups like rasam/dal/sambar, also used for ayurvedic preparations like Kashayam/Arishtam,etc. Tinning called ‘Kalai’ in north India. Chemically Tin much more inert compared to bell-metal and does not corrode at all. But Tin has a very low melting point hence water should always be in contact with Tin, else the metal coating will melt away. Can be used only for making soups, cannot be used for dry/semi-dry cooking or cooking with oil/frying, etc.

4) Cast Iron: Ideal for cooking with oil(frying), and cooking with ghee. Cast Iron also ideal for for roasting/dry cooking like making Dosa,Chapati. I assume Taila and Ghrita most ideally should be made in cast iron vessel. Also Cast Iron(Loha) is not Stainless Steel!! even though both contain Iron. Cast Iron and Stainless Steel exhibit quite different medicinal and thermal properties!!

5) Clay: For those poor people who cannot afford Bell-metal/Brass due to due high cost of Copper and Tin, can use clay cooking pots. Clay also good for storing water just like Copper.

6) Besides the above metals and clay, certain special stone vessels also used for cooking, but I don’t have much idea about those.

Vessels for storing and serving food:
1) Glass is the cheapest and one of the best materials for storing and serving food.
2) China-ware or Traditional Chinese ceramics. Very good for storing/serving food but costly!!
3) Bell-Metal vessels very good for storing/serving food.
4) Tin coated brass vessels also very good for storing/serving food.
5) Clay also good for storing/serving food.

Plastics/Stainless Steel generally to be avoided for serving/storing food. Stainless Steel could be used for storing/serving food when coated with a layer of Tin.

Besides cooking vessels even using cosmetics like soap,shaving cream,shampoo,etc can be injurious to health. It is better to bath using only sesame oil + bath powder like Shikakai or Gram flour.

So using traditional cooking vessels along with avoiding cosmetics like soap for bath and using oil+shikakai for bath can go a long way in curbing modern diseases like cancer and other modern diseases. Since Ayurveda isn’t mere herbalism/ mineral medicines but is also a way of life, such important aspects like bathing cosmetics, toxic cooking vessels cannot be ignored when trying to cure lifestyle diseases.

Dr J V Hebbar MD(Ayu) says:

Thanks for insightful inputs.

Forgot to add that washing vessels is preferably to be done with soapnut powders like shikakai and reetha only. Synthetic dishwashing liquid/bars/powders are to be avoided as they leave a residue in the vessels which can enter into the food being cooked.

Also forgot to add that cast iron vessels should not be used for water based cooking of soups like dal,sambar,rasam, as Water and Iron are incompatible. Also Iron rusts when it comes in contact with water. Cast iron vessels should only be used for making chapati,dosa. And for stir frying vegetables. Deep frying using oil. And also ghee based cooking.

For cleaning cast Iron vessels, after cleaning with shikakai powder, the iron vessel should be heated in a stove till all the water evaporates, as keeping the iron vessel inside with moisture, it may rust.