Hello Melissa -- Coins like yours are often difficult to identify precisely. By the 1700s Spain had colonized much of the New World (North and South America) and she issued many coins in various places, most of which look very similar except for small, minor differences.
Your coin comes from the time of the reign of King Fernando, 1746 to 1759, and these coins are quite rare. Coins with other dates have other kings. This page applies to Fernando coins only.
NEVER CLEAN A COIN. CLEANING RUINS VALUE.
Because you have a valuable coin, you need to be sure you don't have a counterfeit, which abound with these types of coins. You can see an example of an obvious counterfeit at this CoinQuest link, and a not-so-obvious one at this link. Write to us if you need more information about counterfeits. Counterfeits are worth zero.
These gold coins come in five basic denominations, with diameters and gold weights as follows:
1/2 ESCUDO, 15 mm diameter, 0.05 troy ounces gold
approximate collector premium: $50 US dollars
1 ESCUDO, 18 mm diameter, 0.10 troy ounces gold
approximate collector premium: $80
2 ESCUDOS, 22 mm diameter, 0.20 troy ounces gold
approximate collector premium: $100
4 ESCUDOS, 30 mm diameter, 0.40 troy ounces gold
approximate collector premium: $1000
8 ESCUDOS, 35 mm diameter, 0.80 troy ounces gold
approximate collector premium: very rare, premiums can rise over $5000
To find an approximate value for your coin, first look up the current price of one ounce of gold at a site such as kitco.com. Then multiply the current price by the fraction in the list above. This gives the basic gold value. To that value add our approximate collector premium which accounts for the demand collectors place on these beautiful coins.
If you have a genuine, high value piece, you should have it authenticated, graded, and sealed in a hermetic case by one of the following services: PCGS, NGC, ICG, ANACS. Look them up on the Internet. Do not use other services. At a minimum, have your coin looked at by a knowledgeable collector or professional coin dealer.