Babies and young children wear christening or baptism gowns when they are baptized. The yellowing on a white fabric like a baptism gown comes from oxidization or exposure to light. Some fabrics like silk start to turn yellow when exposed to too much natural light. Other fabrics start to yellow from exposure to oxygen over time, which is why yellowing is often associated with age. Baptism dresses hold emotional significance and are often passed down from one generation to the next. The age of these dresses often means yellowing. There are different opinions about the best and most effective way to remove yellowing from a baptism dress. Take your dress to a professional cleaner if you are looking for the safest choice or dealing with a delicate fabric. However, if you want to get the yellowing out yourself, there are a couple of different soaking methods you can use.
Wash the dress using a whitener/brightener. An optical brightener is actually a dye that absorbs light. The fabric reflects more blue light to counteract the yellowing, making it appear whiter and brighter, a process also known as bluing. This method is an option for sturdier fabrics that you can wet-clean.
Soak the dress in a bleach solution. Bleach works wells on sturdy fabrics such as cotton. Use enough warm water to cover the dress in the container of your choice. Add between a 1/2 cup and 1 cup of bleach along with a little bit of detergent. Let the dress soak in the solution and agitate the dress from time to time in the water to ensure that there are no creases. Cotton is also durable enough to stand up to stain-fighting detergents such as OxiClean. Soaking the dress in a container also allows you to check the progress of the fabric. Continue to check on the fabric as you start to see it work. When it has reached the desired whiteness, rinse it thoroughly two or three times and hang to dry. If you want to bleach wool, try using hydrogen peroxide instead of bleach.
Take the dress to a professional cleaner. If your dress is made of a delicate fabric such as silk that does not hold up well to regular cleaning, you need the experience of a professional who can work to remove the yellowing without harming the fabric.