Solution for Glass Blooming

Weatherization of Glass (Bloom)

The term weatherization (or “bloom”) refers to a milky, hazy or crystalline (snowflake) residue on the inside of soda-lime glass. Although at worst an aesthetic issue, the phenomenon is often a concern for customers. As a result, Qorpak Salespersons must be ready and able to address specific customer concerns regarding this problem. Specifically, Salespersons must be aware of the chemical processes involved in the formation of weatherization, as well as the environmental conditions in which it is most likely to occur. Fortunately, the effect of weatherization is often minimal upon the overall quality of the glass, (although certain issues may arise regarding the pH levels of the content of the containers, depending upon specific chemical formulas). Since weatherization is often easily treated, a thorough understanding of the cause of weatherization will allow salespersons to address customer concerns in an effective manner. Ideally, customers should be made aware of this phenomenon, its causes, as well as treatment methods prior to purchase so as to avoid issues at a later date.

Bloom hollow Glass

Clear Hollow Glass without bloom

Chemical Components of Weatherization

·         Weatherization is essentially the formation of carbonate crystals on the surface of the glass. These carbonate crystals are most often Sodium Carbonate (Na2CO3), but can also be composed of Calcium Carbonate (CaCO3).

·         The amounts of Sodium and Calcium Carbonate in soda-lime glass vary greatly, but Sodium Carbonate is always in greater abundance and disassociates more easily. This results in a greater proportion of Sodium Carbonate in the bloom.

·         Soda-lime glass is considerably hygroscopic (water-loving). Water can easily form and accumulate on the glass surface (particularly the inside surface), then be absorbed and remove large quantities of Na⁺ and Ca²⁺ ions. These ions easily reform and collect as carbonate crystals on the surface of the glass as the water is evaporated in the presence of carbon dioxide (CO²)

·         The quantities of Sodium Carbonate and Calcium Carbonate build-up on the surface of the glass are relatively small considering the appearance they leave. Both have a strong tendency to “disappear” when the glass is filled. It may be that the carbonate crystals actually dissolve or that they remain but are not be visible due to their contact with the liquid. Sodium Carbonate, in particular is very water-soluble, and thus aqueous (water based) solutions added to the glass will easily dissolve this carbonate residue.

·         It is important to note that even before bloom is visible, there may be very small quantities of surface carbonate present.

Environmental Causes

·         Humid conditions and changes in relative humidity and temperature affect the amount of atmospheric moisture that the glass is exposed to during storage and shipment.

·         Changes in these conditions also affect the “cycling” of condensation and evaporation. For example, ocean-bound freight has a tendency to be exposed to more humid conditions, both local (actual storage conditions) and atmospheric. For this reason, glass exposed to these conditions may develop bloom more quickly.  It does not, however, have anything to do with the “salt in the air” or salt water conditions.

·         The shape of the glass itself may also affect this process.

·         The size of the opening and the ratio of the inside surface to the opening help determine how much air exchange occurs. Packaging influences the evaporation / condensation cycle as well by limiting air exchange and holding in moisture.

Further Considerations

There is no guarantee as to when weatherization will occur, and likewise there is no true “bloom-free” period for glass. Depending on these conditions, and on the actual carbonate content of the glass, weatherization can develop over a very short period of time or may not be visually noticeable for years. It is important to note, though, that under controlled storage conditions, glass used as soon as possible after manufacture is less prone to the appearance of bloom.

Effects of Weatherization

·         There is a general consensus that surface presence of these carbonate crystals will not affect the vast majority of products.

·         However, it is possible that the release of Sodium Carbonate crystals into certain solutions could increase the alkalinity, and therefore has the potential to raise the pH of the contents of the container.

·         Although the vast majority of products should be unaffected by exposure to weatherization, historically it is not recommended to pack Gin or Ammonia products in glass containing bloom.

·         It is each customers’ responsibility to consider the potential of the finished product exposure to determine the effect (if any) on their product.

Bloom Treatment

·         Treating the surface of the glass with Fluorine Gas will make the surface of the glass more chemically inert (up to ten times) and therefore significantly reduce the rate and amount of bloom that forms.

·         In chemical and analytical applications where even the smallest amount of surface carbonate is considered problematic, Borosilicate Glass is typically used because of its resistance to the formation of Calcium Carbonate and Sodium Carbonate surface crystals.

Ultimately, there are no guarantees when it comes to the appearance of weatherization; as the name implies, it is dependent on environmental storage conditions. In most cases, timely use of the glass is the best defense. Customers should be aware that the “material” comprising the “haze” is always present in the glass; it does not come from an outside source of contamination. Customers should also be aware that in almost all cases the weatherization disappears when the glass is filled. If customers should desire to pursue further treatments, Fluorine Gas can make the glass more inert and reduce the amount of weatherization, or at least delay when it becomes noticeable. If there is a true technical reason that customers need to avoid weatherization, they should consider using Borosilicate Glass.