Bouquet Enterprises

Bouquet Enterprises Outsources Process to Reduce Hazardous Waste and Employee Exposure

Best Alternative to Using Selenius Acid is Outsourcing

Bouquet Enterprises manufactures over 600 different decorative products and gifts. Some of their products require the metal parts to have a rustic appearance. Sheet metal is given this aged look through an antiquing or blackening process which uses selenious acid.

Incentives for Change

The selenium-based acid is hazardous to employees and must be disposed of as a hazardous waste. The sewer system in Kellogg cannot handle heavy metals, including selenium from Bouquet. The overall efficiency of the blackening process needed to be improved.


The MnTAP intern identified three main options to improve Bouquet’s blackening operation.

Option 1: Optimizing use of selenium-based acid

The first step is to use a more appropriate selenium- based acid solution. The chemical solution identified by the intern is specifically designed for the type of sheet metal that Bouquet blackens. The concentrate is diluted in water and used at room temperature to produce the desired appearance.

Optimize concentrations. The current process can be optimized by keeping the chemical concentration of the process bath at the lowest possible operating level. This minimizes losses from dragout—chemical clinging to the part and being removed from the bath. By optimizing the chemical ratio, Bouquet would reduce their chemical consumption by five to ten percent, saving $5,600 annually on chemicals. A few procedures would need to be added, including testing the solution concentration periodically, having a schedule for adding more solution to the bath and filtering the solution bath on a regular basis.

Withdrawal and drain times. Increasing withdrawal and drain times allows more solution to remain in the bath and minimizes the amount of solution contaminating following stages.

Spray rinse and a racking system. A spray rinse system would replace the current rinsing dip tank. Bouquet could reduce waste by 75 percent, saving $6,000 to $11,000 annually in off-site disposal fees.

A racking system would allow up to thirty sheets to be blackened at one time. The rate of production would triple; even greater efficiencies could be attained with more racks.

The cost of the spray rinse tub was too high, making this option unfeasible.

Ion exchange system. Having an ion exchange system for the rinse water will eliminate the stage’s hazardous waste and its disposal fees. The deionized water could be reused in the rinsing process instead of sewered, reducing overall water use.

Potential savings: Reduces waste by 660 gallons and saves 180 gallons of raw material a year. Estimated savings of $14,300 a year.

Option 2: Substituting a non-selenium based acid

A non-selenium based acid could be used to blacken iron and steel. This system uses no U.S. Environmental Protection Agency regulated chemicals, making sewer disposal a potential option. Hazardous waste and the need for an ion exchange system would be eliminated.

This option posed two problems. A stronger acid was required, raising concerns about employee safety. Also, tests of this product indicate that the appearance of the metal from this process is not acceptable. Instead of looking rustic, the metal looks shades of red, purple or blue.

Option 3: Outsourcing

Outsourcing may be the most economical way for Bouquet to manage their blackening process. They would not have to worry about spent chemical from the solution bath, the risks to employees and the liability of handling the acid. A facility with a high production rate will have better economies of scale than Bouquet, resulting in a lower cost per part for blackening.

Potential savings: Reduces waste by nearly 1,000 gallons and saves an estimated $6,000 a year.

Low cost for chemicals
Larger coverage per gallon
Solution bath only needs replenished periodically
Reduced liability
Larger coverage per gallon
Low capital investment
Disposal costs eliminated
Lower cost per sheet
Eliminates liability
No capital investment
Disposal costs eliminated
Capital investment
Disposal costs
Final appearance
Cost of solution
Solution bath needs dumped periodically
Final appearance could vary


As a result of the project, Bouquet decided that outsourcing the process is the most effective way to handle this hazardous material problem. They are currently outsourcing half of the products requiring blackening. Bouquet plans to outsource the entire process once they have worked out all the issues related to quality.

When considering outsourcing, Bouquet had to work with the service provider to match their color requirements and make the process more efficient. Initially the parts were batch processed, resulting in an inconsistent appearance. They worked with a vendor to develop a racking system to keep parts separate when dipped into the bath. As a result, quality is acceptable and consistent, and costs decreased by 75 percent.

Because Bouquet still has half of the process in-house they optimized their acid baths and developed clear instructions to let employees know when recharging the baths is necessary.

This project was conducted in 1997 by MnTAP intern Tony Smook, a composite materials engineering student at Winona State University