Comparison of Different Clear Finishes
Clear finishes are intended to make wood look good and meet the demands to be placed on the finish. Choosing a clear finish for wood involves trade-offs between appearance, protection, durability, safety, requirements for cleaning, and ease of application. The following table compares the characteristics of different clear finishes. 'Rubbing qualities' indicates the ease with which a finish can be manipulated to deliver the finish desired. Shellac should be considered in two different ways. It is used as a finish and as a way to manipulate the wood's ability to absorb other finishes by thinning it with denatured alcohol. The alcohol evaporates almost immediately to yield a finish that is completely safe but shellac will attach itself to virtually any surface, even glass, and virtually any other finish can be used over it.
| Appearance | Protection | Durability | Safety | Ease of Application | Reversibility | Rubbing Qualities | |
|---|---|---|---|---|---|---|---|
| Wax | Creates shine | Short Term | Needs frequent reapplication | Safe when solvents in paste wax evaporate | easy, needs sanding | Can easily be removed with solvents | Needs to be buffed |
| Shellac | Some yellow or orange tint, depending on grade used | Fair against water, good on solvents except alcohol | Durable | Safe when solvent evaporates, used as food and pill coating | French polishing technique difficult to master. | Completely reversible using alcohol | Excellent |
| Nitrocellulose lacquer | Transparent, good gloss | Decent protection | Soft and somewhat durable | Uses toxic solvents. Good protection is needed, especially if painted | Requires equipment. | Completely irreversible | Excellent soft finish |
| Conversion varnish | Transparent, good gloss | Excellent protection against many substances | Hard and durable | Uses toxic solvents, including toluene. Breathing protection is needed | Requires spray equipment. Used in professional shops only | Difficult to reverse | Excellent hard finish |
| Linseed oil | Yellow warm glow, pops grain1, darkens with age | Very little | Fairly durable, depending on number of coats | Relatively safe, metallic driers are poisonous | Easy, apply with rags and wipe off. Takes relatively long time to dry | Needs sanding out as oil is absorbed | None |
| Tung oil | Warm glow, pops grain1, lighter than linseed | Water resistant | Fairly durable, depending on number of coats | Relatively safe, metallic driers are poisonous | Easy, apply with rags and wipe off. Faster to dry than linseed oil | Needs sanding out as oil is absorbed | None |
| Alkyd varnish | Not as transparent as lacquer, yellowish/orange tint | Good protection | Durable | Relatively safe, uses petroleum based solvents | Brush or spray. Brushing needs good technique to avoid bubbles & streaks | Can be stripped using paint removers | Fair |
| Polyurethane varnish | Transparent, many coats can look like plastic | Excellent protection against many substances, tough finish | Durable after approx. 30 day curing period | Relatively safe, uses petroleum based solvents | Application requires some level of skill | Can be stripped using paint removers | Bad, coats do not meld leading to white rings if rubbing out cuts through coat |
| Water-based polyurethane | Transparent | Good protection. Newer products (2009) also UV stable | Durable after approx. 10 day curing period | Safer than oil-based, fewer volatile organic compounds | Brush or spray. Fast drying demands care in application techniques | Can be stripped using paint removers | Bad, coats do not meld leading to white rings if rubbing out cuts through coat |
| Oil-varnish mixes | Similar to oils unless many coats applied, then takes on characteristics of varnishes | Low, but more than pure oil finishes | Fairly durable, depending on number of coats (archaic product, rarely used due to availability of modern finishes) | Relatively safe, uses petroleum based solvents | Easy, apply with rags and wipe off. Faster to dry than linseed oil | Needs sanding out as oil is absorbed | None unless many coats applied |
1 accentuates visual properties due to differences in wood grain.
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