Lead to Gold

"Converts Lead Bloons to GOLD! Special solvents do extra damage to Lead Bloons, destroying them in one shot and generating cash."

- Bloons TD 6 description.

Lead to Gold is the third upgrade of Path 3 for the Alchemist in Bloons TD 6. As stated in its name, it turns Lead Bloons into Gold when attacked by this Alchemist's acid attacks, rewarding $50 cash once the lead layer is popped. Because Lead to Gold has a +9 damage buff on lead-type Bloons, including DDTs (if granted with camo detection), Lead Bloons, including fortified, are instakilled. This upgrade cannot gain cash from popping DDT layers, despite being compatible with the damage increase towards lead bloons.

It costs $850 on Easy, $1,000 on Medium, $1,080 on Hard, and $1,200 on Impoppable.

Strategies
Lead to Gold causes the Alchemist to be able to generate a secondary income to popping Bloons when combating Leads, granting a fixed $50 ($25 on Half Cash) for every Lead bloon popped and destroying the bloon entirely. As long as the Alchemist's acid touches the Lead Bloon, the Lead will be instakilled and immediately apply the income bonus. While the upgrade is 20% cheaper than even a Banana Farm, the upgrade is best used based on context of the round and the towers behind the Alchemist; too few Leads, and the upgrade is unprofitable, too many towers that can already pop Leads and the Alchemist is unable to profit from the remaining Bloons.

Tips

 * To make sure that the Alchemist gets to Lead Bloons first before the other towers, placing him at the beginning of the track allows for more time before other Lead popping towers can even have the Leads in their range.
 * In Magic Monkeys Only games, it can be considered as the primary Lead popping source to be both reliable, profitable and having little competition when using other Magic Monkeys with proper upgrades. However, the one game mode where Lead to Gold shines the brightest is on Apopalypse, where dense groups of Leads are bound to appear often. In some cases, it can be even more profitable than using Banana Farms.
 * Some of the more devastating competition for the practicality of this upgrade are towers with high range or splash that can take out Leads, such as Super Monkeys with Plasma Vision or higher and Bomb Shooters following its first or third paths.
 * The most devastating tower to compete with, however, is Obyn Greenfoot, as he is cheap, often used at the start of the game, boosts the Magic class to interfere with Magic Monkeys Only games and has a long reaching Lead popping attack. Being able to pop the Lead layer of the first Bloons is possible with ideal positioning, but since Obyn's attacks typically follow the track against the Bloons, it can lead to the resulting Black Bloons to receive fire and pop the new Leads before the Alchemist has the chance to.
 * The best game mode to use Lead to Gold in is Apopalypse Mode. In the late stages of gameplay, Lead Bloons become more and more common, allowing you to make a lot of money with just a Lead to Gold Alchemist. Be sure to give the tower camo detection, as almost all late-game Lead Bloons will have camo properties. If possible, also give the Alchemist extra attack speed, so that he doesn't miss any Lead Bloons.
 * In terms of crosspathing, a 1-0-3 alchemist is prefered since it will allow the bigger splash radius of Larger Potions to affect more leads at once, ensuring that the alchemist can profit from as many leads as possible. 2-0-3 would actually go against what Lead to Gold is suppoed to do, as this would now allow any tower to pop leads from any tower, with no addtional income, provided that said tower is in range of the alchemist. If that is not the case, then it's just a waste of money.

Earnings
Lead to Gold is only effective on rounds with Lead Bloons. On Easy, it takes 17 Lead Bloons to earn back the cost of the upgrade. Medium takes 20, Hard takes 22 (44 on Half Cash mode), and Impoppable takes 24. Below is a table listing all of the rounds with Lead Bloons, how many are in each round, and the maximum possible earnings from each round.

Alternate Bloon Rounds
''*The money earned on these rounds may only be obtained if the Alchemist is given Camo detection by another tower, or the camo properties are stripped without popping the Bloons with upgrades such as Shimmer or Bloontonium Reactor without Heat-Tipped Darts.

Trivia

 * The upgrade is a reference to alchemy and the Philosopher's Stone, which turns base metals into precious gold, as seen with how the upgrade works.
 * Alchemy is the ancient protoscience of transforming and purifying materials, often to create gold. However alchemy is far from scientific, as many of its core tenets and goals are simply nonsensical.
 * Scientists have tried and actually achieved turning lead into gold, by the use of nuclear transmutation. By using a particle accelerator, protons and electrons can be removed from lead (atomic number 82) to create gold (atomic number 79) by matching its charge. However, the energy released from transforming stable lead would make the process impractical.
 * Acid pools created by this Alchemist from the Acid Pool upgrade will also trigger the $50 cash reward from popping leads.
 * The same applies to Rubber to Gold, but only works on Leads and does NOT automatically turn other Bloons partially to gold unless the potion directly hits the targeted Bloon.
 * The Lead to Gold Alchemist or its subsequent upgrades do not have to make the final pop in order to activate the $50 per lead effect; it just has to damage the Bloon at least once, which is evident for Fortified Leads. Link.
 * Even though Version 19.0 added a separate money counter for almost all towers, it has not been yet implemented for Lead to Gold, Rubber to Gold, Monkey Town (and by extent Monkey City), Pirate Lord, Support Chinook, and Jungle's Bounty. It has yet to be fully implemented for Spirit of the Forest (ability only), and Sun Temple and True Sun God / Avatar of the Vengeful Monkey with Support sacrifices.
 * Lead to Gold's $50 income per Lead Bloon ($25 on Half Cash) cannot be increased via Monkey City or any other buffs.
 * There was a bug in Version 23.0 where adding Path 2 upgrades to Lead to Gold does not receive the lead damage buff. This was fixed in Version 23.1.
 * Double Cash doubles the earnings from Lead to Gold, earning $100 per Lead Bloon.
 * Benjamin's Bloon Trojan ability also increases cash from leads.