How to Make a Chromic Acid Plating Solution

eHow may earn compensation through affiliate links in this story.

Chromic acid plating solution is used in the electroplating of metals for making surfaces decorative and corrosion resistant. There are several recipes for making the plating solution. The ingredients of the most common electroplating bath include chromium trioxide and sulfuric acid. The ratios of these chemicals in the recipe vary depending on the objective of the plating. There are "hard plating" and "decorative plating" recipes that have different ratios of chromic acid to sulfate. Some bath solutions include flouride catalysts which increase the rate of chromium deposition.


Chrome plating with chromic acid solutions provides a corrosion-resistant metal surface.

Things You'll Need

  • Rubber Gloves

  • 5 Ml Pipet

  • Sulfate Test Kit

  • Distilled Or Deionized Water

  • Pipet Bulb

  • Plastic Container For The Acid Bath

  • 100 Ml Graduated Cylinder

  • Weighing Scale

  • Face Shield

  • Weighing Paper Or Boat

  • Rubber Or Plastic Apron

  • Chromium Trioxide Crystals

  • Container For Measuring Volume In Liters

  • Sulfuric Acid

Step 1

Fill the bath container to the halfway mark with distilled or deionized water and calculate the amount of chromium trioxide and sulfuric acid to be added to the solution. For decorative plating, add 300 grams per liter of chromium trioxide and 3 grams per liter of sulfate. For 50 percent sulfuric acid, you will need to 61 milliliters per liter of bath solution to achieve this sulfate concentration.


Video of the Day

Step 2

Weigh the the amount of chromium oxide needed and add it to the water in the electroplating tank. Measure the amount of 50 percent sulfuric acid that is needed and add it slowly to the tank. Gently stir the bath tank solution to assure that all of the chromium oxide crystals dissolve into the solution.


Step 3

Transfer by pipet 2.5 milliliters of the electroplating solution to a 100 ml graduated cylinder that has 97.5 ml of deionized water to make a dilution. This dilution is necessary because the testing range of the testing kit for sulfate, given in the references below, is 50-200 milligrams per liter.


Step 4

Mix the solution in the graduated cylinder with a plastic or glass rod. Filter the solution before testing if there is sediment or suspended particles. Then perform the sulfate test according to the instructions of the test kit.

Step 5

Multiply the results of the test kit by 40 to arrive at the grams per liter of sulfate in the electroplating solution. Adjust the concentration if needed.


Hard plating processes use a chromic acid to sulfuric acid ratio of 155-200:1. Decorative plating use ratios from 100-125:1

Convert grams per liter to avoirdupois ounces per gallon by multiplying by 0.133.

Addition of fluoride catalysts to the bath will double the rate of chromium deposition.

If there are particulates in the solution for sulfate testing, it must be filtered prior to analysis.

If the level of sulfate becomes to high, barium carbonate can be used to precipitate out the sulfate. Barium sulfate is formed.


Wear protective equipment when working with sulfuric acid and chromium trioxide.

Pour acid into water slowly. Never pour water into acid.

Ventilation in the area of the electroplating bath is necessary because hydrogen gas is produced in the process.


references & resources

Report an Issue

screenshot of the current page

Screenshot loading...